Data communications preprocessor
CROSS REFERENCE TO RELATED APPLICATIONS 
     The microprogrammable data communications preprocessor of the present invention cooperates in a data communications system employing a microprogrammable central processing unit. In the preferred embodiment, the central processor is of the type disclosed in copending application Ser. No. 825,569 for &#34;Polymorphic Programmable Units Employing Sub-Instruction Sets&#34; filed May 19, 1969 in the name of U. Faber et al. Further, the preferred embodiment utilizes a central processing unit having a port select unit (PSU) of the type disclosed in copending application Ser. No. 392,116 for &#34;Dynamic System Firmware&#34; filed Aug. 27, 1973 in the name of K. Kistler et al. 
     The data communications preprocessor of the present invention employs a microprogrammable serial byte microprocessor of the type disclosed in U.S. Pat. No. 3,878,514 issued to U. Faber on Apr. 15, 1975 for an &#34;LSI Programmable Processor&#34; filed Nov. 20, 1972. More specifically, the preferred embodiment of the present invention uses an improved version of the Faber processor of the type disclosed in copending application Ser. No. 455,060, now U.S. Pat. 3,972,024, for &#34;An Improved Programmable Microprocessor&#34; filed Mar. 27, 1974 in the name of F. Schroeder et al. 
     The above-cited cross references provide much useful technical and background information which is not unnecessarily repeated in the present specification. Therefore, a review of these cross references will aid in an understanding of the present invention. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a microprogrammable preprocessor for interfacing between a multiplicity of data communications lines and a central microprogrammable processor by tending to the detailed line procedures and requiring central processor intervention on a message basis only. 
     A data processing communications system generally includes a central processing unit (CPU) and a plurality of data communications channels including direct connect lines, MODEMS, and the like. As the system becomes more complex, inefficiencies increase as the CPU data processing functions are interrupted more frequently for line procedures and data communications details. The addition to the system of a microprocessor to handle line procedures and details may relieve the CPU of these burdens but may otherwise limit the data communications aspects of the system to the necessarily limited capabilities and throughout speed of the microprocessor. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Therefore it is an object of the present invention to provide a high speed, flexible, data communications preprocessor. 
     It is a further object of the present invention to provide a microprogrammable data communications preprocessor for use with a microprogrammable CPU in a data communications system. 
     A data communications preprocessor constructed in accordance with the present invention includes a line adapter associated with each data communications line for interface purposes, a scratch pad memory for storing the data line parameters of each data line and a microprogrammable serial byte microprocessor for exercising detailed control over a plurality of data communications lines while requiring central processor intervention on a per message basis only. Operational speed is enhanced through a direct memory access channel which permits data transfer directly from the preprocessor to the main memory of the central processor, and through the inclusion of automatic operation logic which effectively by-passes the serial byte microprocessor for an automatic transfer of two bytes of data. 
    
    
     The system configuration and operational details given above have been presented in simplified form. Other objects, features, and advantages of the invention will be apparent from the following description of the preferred embodiment of the invention and the accompanying drawings thereof. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a data communications system using the data communications preprocessor of the present invention; 
     FIG. 2 is a block diagram of the data communications preprocessor of the present invention; 
     FIG. 3 is a diagram of the scratch pad memory used in the preprocessor of FIG. 2; 
     FIG. 4 is a more detailed diagram of the preprocessor of FIG. 2; 
     FIG. 5 is an illustration of the word format of transmit status, receive status, line frequency select, and adapter descriptor control words; 
     FIG. 6 is a representation of the data paths and logic functions of the preprocessor of FIG. 4; 
     FIG. 7 is a representation of an adapter I/O register used in the preprocessor of FIG. 4; 
     FIg. 8 is a representation of the status words and bit isolation unit used in the preprocessor of FIG. 4;. 
     FIG. 9 is an illustration of the scratch pad memory addressing and control instructions used for the scratch pad memory of FIG. 3; 
     FIG. 10 is an illustration of the adapter descriptor register which serves to define the functional operation of the adapter; and 
     FIG. 11 is an illustration of the data set description register which serves to define the functional operation of the data set. 
    
    
     GLOSSARY OF ABBREVIATIONS AND ACRONYMS 
     Following is a listing of abbreviations frequently used in the detailed description of the preferred embodiment of the invention and related cross referenced. 
     
         ______________________________________                                    
A0 - A4         SPM Address (Char.)                                       
ADDOUT          Adder Output                                              
ADPCLR          Adaptor Clear                                             
AOV             Adder Overflow                                            
ASF             Auto Sequence                                             
ADF.D/                                                                    
                 ##STR1##                                                 
ASYNCLK n/      Asynchronous Clock (To Adaptor)                           
AUTOOP          Auto OP Time                                              
BA 2F/          ASF 2nd Char. Time                                        
CDSCLKPn        CPU Clock                                                 
CLBMIRO3        MIR Bit 3                                                 
Compel/         Compute Delay                                             
CPIN            CLK Pulse                                                 
D/              Auto OP 2nd Char. Time                                    
DATAIN          MPU Data Input                                            
DATAO           MPU Data Output                                           
DATARD/         Read Data to CPU                                          
DDPDESn         Enable Adaptor n Descriptor                               
DEVOF           Device 0                                                  
DEFIF           Device 1                                                  
DEV3F           Device 3                                                  
DEVWT/          Device 1 and SPM Write                                    
DIRO/ - DIR 7/  Adaptor I/O Bits                                          
DMARD           DMAC Read From CPU                                        
DMAWT/          DMAC Write to CPU                                         
DTR             Data Terminal Ready                                       
ENSYN           Enable Sync Detect                                        
EXT             MPU External Interrupt                                    
EXTEN           Enable External Bus                                       
EXT 01/ - EXT 16/                                                         
                External Bus                                              
FCD 000-111     Function Control Register                                 
                (FCR) Operation Codes                                     
LAST SB         Last Strobe                                               
LUMIR01/-LUMIR 16/                                                        
                MIR Bus                                                   
MAR DATA        MAR Data (card to card                                    
                and serial)                                               
MAR OUT         MAR Output (serial)                                       
MAR SEL         MAR Serial Input Enable                                   
MD01/ - MD 12/  MPM Memory Data                                           
MDR DATA        MDR Data                                                  
MDR OUT         MDR Output (serial)                                       
MDR SEL         MDR Serial Input Enable                                   
PAGE 1/         Page Select in SPM                                        
PE              Parallel Enable (MAR &amp; MDR)                               
PRESB           Prestrobe                                                 
PRESBD          Prestrobe Delayed                                         
PSINSTn         Instruction Bit from CPU                                  
PS READn        CPU Read                                                  
PS WRITEN       CPU Write                                                 
RASF            Reset ASF                                                 
RQ/             Request                                                   
RQSTL/          Request to Steal                                          
RST/            Request to Send                                           
SELDATA         MDR or MAR, Data Output                                   
SETASF/         Set Auto Sequence                                         
SETDES          Data Set Descriptor Enable                                
SINT/           Status Interrupt to CPU                                   
SIOOUT/         SPM I/O SErial Output                                     
SMADR 01/-SMADR 16/                                                       
                CPU Memory Address                                        
SPMIN0-SPMIN7   SPM Input Bits                                            
SPM OUT 0/-SPMOUT 7/                                                      
                SPM Output Bits                                           
STINT/          Soft Status Interrupt From CPU                            
STLG            Steal Granted                                             
WRITE           CPU Write                                                 
WT/             SPM Write                                                 
XCLK            Transmit Clock                                            
XDATA           Transmit Data                                             
XMITSB          Transmit Strobe                                           
XMITST          Transmit Status Enable                                    
XMODE           Transmit Mode                                             
1st OUT         1st Output of Auto Sequence                               
______________________________________                                    
 
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, the data communication preprocessor, hereinafter called the DCPP 11, of the present invention provides the data communications interface between the central processing unit CPU 13 and multiple data communications lines 15. The data communications interface is with either standard data sets 17 or direct connect lines, and include full duplex, half duplex, synchronous, and asynchronous applications. Each data communication line 15 serviced requires an individual line adapter 19. Each line adaptor 19 contains the transmit and receive logic necessary for transferring data to and from the data communication line 15, and the logic required to control the communication interface, both for normal operating control and status interrogation. 
     The DCPP 11 incorporates its own microprocessing unit, hereinafter called the MPU 21, which permits the DCPP 11 to operate in a semi-autonomous mode relative to the CPU 13. The MPY performs many of the functions normally required of a control processor, thus relieving the CPU 13 of much of the burden associated with detailed control of the DCPP 11. The MPU 21 is loadable with commands from the CPU 13 via a DCPP 11 microprogram memory, hereinafter called the MPM 23. The MPU 21 utilizes these commands to generate the internal firmware set used for DCPP 11 function control. Thus, the functional characteristics of the DCPP 11 are determined by the program loaded from the CPU 13. A direct access channel 25 provides for information transfer directly between the direct memory access logic, hereinafter called the DMA 26, in the DCPP 11, and the main memory 28 of the CPU 13. This direct transfer further reduces the need for the CPU 13 intervention. 
     The DCPP 11 interface 27 with the CPU 13 is via a port select unit, hereinafter referred to as the PSU 29, contained within the CPU 13. The PSU 29 controls and synchronizes the interface 27 between the CPU 13 and DCPP 11. The DCPP 11 acts upon control words from the CPU 13, performs the specified operation, and upon completion of the operation, generates and returns a status word containing operation status and/or error status information. 
     The primary features of the DCPP 11 are itemized as follows: 
     1. Multiple data communication lines are serviced concurrently requiring central processor unit CPU 13 attention only a per message basis. 
     2. Line procedures are handled without CPU 13 intervention. Line procedures are defined by the DCPP 11 microprogram thereby providing application flexibility. 
     3. Direct memory access enables the DCPP 11 to handle message transfers without intervening the CPU 13 attention; the CPU 13 is notified upon message transfer completion. Buffer area is assigned in the main memory 28 for each line. Buffer size and location is specified by the CPU 13. 
     4. Upon exceeding a specified number of retries for a message, or upon line failure, the DCPP 11 status word is up-dated accordingly and the CPU 13 is interrupted. Failure on one line will not effect transactions on another line. 
     5. The data communications line adaptor 19 is designed to interface with the standard data sets 17 or direct connect line including full or hald duplex, synchronous or asynchronous applications. Standard baud rates from 75 to 19.2K baud are programmably selectable. The data communication line adaptor 19 can be preset for most line requirements by programmatic control. 
     FIG. 2 is a functional diagram of the DCPP 11. The diagram shows the following functional blocks: 
     The CPU 13 interface logic 31, the loader 33, the MPM 23, the MPU 21, the function control logic 35, the microprocessor support logic 37, the direct memory access logic 26, and the universal line adaptor 19. Each of these functions is briefly described below. 
     The CPU interface logic 31 allows the CPU 13 to load or modify the contents of the memory MPM 23. This provides the CPU 13 with complete control over the program contents of the MPM 23 memory. The CPU interface logic 31 permits the CPU 13 to direct DCPP 11 operations such as transmit data, receive message, disconnect line, etc. The CPU interface logic 31 also allows the DCPP 11 via status interrupt to report status to the CPU 13. 
     The loader logic 33 is used only when the CPU 13 loads or modifies the DCPP 11 microprogram memory MPM 23. The CPU 13 selects load mode via a control word register. In load mode, random or sequential loading of the microprogram memory MPM 23 is possible. 
     The MPM 23 stores program information for the microprocessor MPU 21. The storage capacity is expandable in the preferred embodiment from 2k to 6k words, in 2K word increments. Each word consists of 13 bits (12 data bits plus one parity bit). 
     The microprocessor MPU 21 controls the operations of the DCPP 11. It initiates and executes line message transactions and special functions as directed by the CPU 13. When a plurality of lines are active, the microprocessor MPU 21 will sequentially interrogate each line adaptor 19 and provide service on an as-requested basis. In the preferred embodiment the microprocessor MPU 21 contains an eight bit wide arithmetic unit and performs instructions at a one megaHertz rate. 
     The function control logic 35 allows the microprocessor MPU 21 to address and transfer information to and from other functional units including up to four line adaptors 19. 
     In the microprocessor support logic 37, a scratch pad memory 39 provides temporary data storage for the microprocessor MPU 21. The scratch pad memory 39 is used to store information for each data communication line 15 such as buffer location in current address, line procedure details, job description, current status, etc. Thus, the scratch pad memory 39 is used by the microprocessor MPU 21 to keep track of what the DCPP 11 is doing. In the preferred embodiment the scratch pad memory 39 is expandable as the number of data communication lines 15 is increased. A storage capacity of up to 128 bytes per data communication line 15 is provided. The microprocessor support logic 37 also includes the automatic operation logic 43. 
     The direct memory access (DMA) logic 26 provides the DCPP 11 with a direct access path to the main memory 28. The main memory 28 is used for message input and output buffering for each data communication line 15. In addition, the main memory 28 is used to store control and data descriptors for each data communication line 15. The main memory 28 which is accessed both by the CPU 13 and the DCPP 11 is used as the transfer medium for the exchange of data and control of result descriptors. 
     The data communication line adaptors 19 provides the interface between the DCPP 11 and the data sets 17 or direct connect lines. An individual line adaptor 19 is required for each data communication line. It contains transmit and receive logic 45 capable of operating at selectable baud rates, synchronous or asynchronous and full or half duplex. The microprocessor MPU 21 controls the functional operation of the data set 17 and line adaptor 19 by means of control descriptors. The microprocessor 21 interrogates the line adaptor 19 status and the data set 17 status by reading the respective status register in the included data set control and status logic 47 and the adaptor control line status logic 49. 
     The DCPP 11 with its own microprocessing unit 21 is a programmable multiline control device dependent port (DDP). In combination with a CPU 13 an overall data communications system consists of two processors, each able to operate independently by containing an interpreter and program within its own memory. The first processor, the CPU 13, has control of the usual peripherals whereas the second processor, the DCPP 11, controls up to four data communication lines 15. Since the processor DCPP 11 is microprogrammable a program language, NDL (network definition language) is provided in the preferred embodiment to handle the data communication aspects. In order that data received by the DCPP 11 can be, for example, printed, there has to be a means of communications between the DCPP 11 and the CPU 13. When a message is received by the DCPP 11 the NDL program will cause it to be stored in an area of the DCPP 11 to which the CPU 13 has access. This may be termed a receive buffer. Likewise, the CPU 13 may desire to read a keyboard message and sent it to a terminal. Therefore, as well as the receive buffer there must also be a transmit buffer. In order that data programs being run may be related in some way, one processor or the other must have ultimate control. The CPU 13 is given this ultimate control. The program it is running is the main program which will, for example, contain data it wishes to send to a data communication line 15 from some peripheral and decide which terminal to send it to. Thus the source language has instructions such as &#34;transmit message to   . &#34; These instructions are decoded by the data communications controller portion of the source language and formatted to suit NDL. This is stored in an area of memory considered the operation buffer. Now it can be clearly seen that the NDL program and the DCPP 11 can investigate an instruction in the operation buffer. Dependent on this instruction it will branch through a specific routine. The NDL instructions within the subroutine will be broken down into microstrings by the NDL interpreter and performed by the hardware. 
     The NDL program is specific to a given network of terminals. It will provide all the necessary controls for that network, determining such things as: is the requested terminal valid, is it already busy, how often should it be serviced, what is its line frequency, what line is it on, etc. Thus the main source language program needs only to say &#34;send this message to terminal   &#34; and NDL along with DCPP 11 does the rest. 
     As part of the pairing-up procedure a warm start is performed wherein the NDL is read from a disc and stored into the DCPP 11 memory. This is done by the usual peripheral control method of control words and data words. Once loaded the DCPP 11 is inhibited from operation until suh time as a program is initiated which requires data communication. 
     When a data communication program is called from disc into the main memory 28, the first part of the load operation loads any soft controllers, followed by a special instruction set of source level data communication instructions. 
     In the preferred embodiment, a set of NDL tables are produced containing information about software to be used (size-location number of entries - size of transmission, etc.), the lines in use (speed-number of stations - delays, etc.), the stations in use (description of terminal - type of parity-frequency-buffer size, etc.), and many other parameters used for operation. Each table also references the location of the next in chain, but this reference is calculated at the NDL program load time. 
     Once loaded, the NDL program will start automatically. It releases the DCPP 11 for operation and selects from the NDL tables the various words frequently used and stores information relating thereto in the internal scratch pad memory 39 for fast access. The information stored contains the reference addresses to the NDL tables, the start address of a microstring to be returned to, the address of the CPU 13 memory of the next NDL instruction, etc. Once the initial process is completed the NDL program goes into idle where it waits for further instructions from the main program. 
     A very important feature of the DCPP 11 is the scratch pad memory 39. With reference to FIG. 3, the scratch pad memory 39 contains in the preferred embodiment 512 one-byte word locations. Since there can be up to four data communication lines 15, and since the memory is divided into four blocks of 128 bytes with one block allocated per line, part of the scratch pad memory 39 addressing is devoted to selecting the direct block of 128 bytes. Each block of 128 bytes is subdivided by page addressing logic 50 into four pages of 32 bytes each. Within a selected page, byte addressing logic 52 selects a specific byte. As will be detailed hereinafter, bits of four bytes in each page may be isolated and selected by further address logic 54. In the preferred embodiment, two pages of scratch pad memory 39 (64 characters or bytes) are required to handle a half duplex communications line and four pages to handle a full duplex communications line. 
     In operation, the DCPP 11 fetches an NDL instruction from the main memory 28 and decodes it into OP code. Performance of the OP code may require data to be transferred to or from main memory 28. This is done by stealing. A status word is used to indicate to the CPU 13 a microprogram memory 23 or a scratch pad memory 39 error in the DCPP 11. If this condition occurs a status interrupt is sent to the CPU 13 and the MPU 21 is inhibited from running. 
     In the initiation of information transfer between the CPU 13 and the DCPP 11, the port select unit 29 decodes the three bit groups from the CPU 13 to completely define the operation that is to take place. The command field (nanobits 51 through 54) establishes whether the operation is to be a device read or a device write. The four least significant bits contain the specific device write, and the most significnt bits in conjunction with the command type distinguishes between control, data, and status words. 
     MAIN PROCESSOR -- PREPROCESSOR INTERFACE 
     The interface between a microprogrammable processor and a microprogrammable microprocessor is not characterized by a complex array of hardwired logic interconnections but rather by the control, data, and status words that the two processors use to communicate with and to control each other. Four basic word formats are used to tranfer control, data and status information between the main processor CPU 13 and the preprocessor DCPP 11. Each word format comprises 16 bits with the first bit designated as the most significant bit (MSB) and the sixteenth bit as the least significant bit (LSB). The four basic word formats are a control word (DW·INST), a write data word (DW·INST), a read data word (DR·INST/), and a status word (DR·INST). The significant bits of the four basic word formats are detailed below. 
     CONTROL WORD (DW·INST). 
     DW·INST allows the CPU 13 to perform the following: 
     Bit 1: Enter or exit load mode. Load mode enables the CPU (via DW·INST/) to load or verify the contents of the MPM 23 or to have the MPU 21 operate using the MIR bus 51 as an instruction source. 
     Bit 2: Clear MPU 21 MPCR. Used only in conjunction with enter or exit load mode. Clear MPU 21 MPCR provides the capability to start loading or execution at either MPM 23 location zero or the current address. 
     Bit 3: Clear DCPP 11. Sets or resets the clear DCPP 11 flip-flop. The clear DCPP 11 if set will hold the DCPP 11 in a cleared state. Once set it will remain set until a command is received to reset it. 
     Bit 4: MTR Override. When set, inhibits SPM 39 or MPU 21 parity errors from shutting off run. 
     Bit 15: Execute mode. Used by MTR to disable writing into MAR 53 and MDR 55 from the MIR but 51 with a data write (DW·INST/). Also, disables MTR request to steal. 
     Bit 16: MTR Mode. 
     Used by MTR for the following: 
     1. Disables MAR select. 
     2. Enables parity error while in load mode. 
     3. Complements MPM 23 parity checkergenerator. 
     4. Gates ASYNCLKO to DINT. 
     5. complements SPM parity generator. 
     DATA WORDS (DW·INST/ or DR·BEX·INST/) 
     A DR·BEX·INST/ will transfer the contents (16 bits) of the MDR 55 into the B-register of the CPU 13. 
     A DW·INST/ will transfer 16 bits of MIR data into MAR 53 and MDR 55. If in load mode, the following functions are also enabled: 
     1. If MIR01 and 02 are both zero than MIR06-16 (12 bits will be loaded into the MPM 23 at the address defined by the MPU 21 MPCR and then the MPU 21 MPCR will be incremented. 
     2. IF MIR01 (EXECUTE INST) is set then MPU 21 will execute the instruction (12 bits) contained in MIR05-16, thus the CPU 13 can single-step instructions to MPU 21 and/or DCPP 11. 
     3. if MIR01/ and MIR02 (MPU 21 to MDR 55) is set then a copy of the instruction in MPM 23 location per MPU 21 MPCR is transferred into the MDR 55 and MPU 21 MPCR is subsequently incremented. This feature is provided to allow the CPU 13 to read and check the contents of the MPM 23 after loading. 
     4. If MIR03/ (MTR STEAL) is set, the CPU 13 will execute an MRT request to steal. This allows CPU 13 to execute a cycle steal independent of MPU 21. The MTR data word (DW·INST/) is defined as follows: 
     
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MTR  EXEC LOAD                                                            
MODE MODE MODE DW INST                                                    
                      MIRO1                                               
                           MIRO2                                          
                                MIRO3                                     
__________________________________________________________________________
1    0    0    1  1   0    0    1                                         
__________________________________________________________________________
 
    
      this mode enables the CPU 13 to generate a steal cycle from a data write. The address is determined by the previous data loaded into MAR 53. 
     5. the MTR parity bit is used by the MIR to bring the parity bit to the MDR 55 and MAR 53 registers for testing. 
     The following listing describes functions of various combinations of control and data words. 
     
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DATA WORDS (DW · INST/ OR DR · BEX · INST/)    
LOAD    DR ·                                                     
MODE DW BEX                                                               
           INST                                                           
               MIRO1                                                      
                    MIRO2                                                 
                         MIRO3                                            
                              FUNCTION DESCRIPTION                        
__________________________________________________________________________
0    1  0  1   1    0    1/0  Enter load mode and                         
                         (note                                            
                              reset MPCR 59, thus                         
                         1)   loading will start                          
                              at address zero. If                         
                              MIRO3 = 1, set                              
                              DCPP 11 clear flip-                         
                              flop.                                       
0    1  0  1   1    1    1/0  Enter load mode, do                         
                         (note                                            
                              not reset MPCR 57.                          
                         1)   Loading will start                          
                              at current address.                         
1    1  0  0   0    0    0    Load data in MIRO5-                         
                              16 (complement) into                        
                              MPM 23 and then                             
                              increment MPCR 57.                          
1    1  0  0   1    0    0    MPU 21 will execute                         
                              instruction contained                       
                              in MIRO5-16 (true).                         
                              MPM 23 is not loaded.                       
1    1  0  0   0    1    0    Transfer a copy of                          
                              instruction from                            
                              MPM 23 into MDR 55                          
                              and MAR 53 and                              
                              increment MPU 21                            
                              MPCR. Note: MIRO5-                          
                              16 must be all                              
                              zeroes.                                     
X    0  1  0   X    X    X    Transfer contents of                        
                              MDR 55 into the CPU 13                      
                              B-register via EXT                          
                              bus 59.                                     
1    1  0  1   0    0    1/0  Exit &#34;load mode&#34; and                        
                         (note                                            
                              clear MPCR 57, thus                         
                         1)   MPU 21 program                              
                              execution will start                        
                              at location zero.                           
1    1  0  1   0    1    1/0  Exit &#34;load mode&#34; and                        
                         (note                                            
                              do not clear MPCR 57,                       
                         1)   thus MPU 21 program                         
                              at current address.                         
0    1  0  0   X    X    X    Load contents of MIR                        
                              (16 bits) into MAR                          
                              53 and MDR 55.                              
X    0  1  1   X    X    X    Read Status word to                         
                              CPU 13 B-register and                       
                              reset STINT.                                
0    1  0  1   0    0    0    Set DCPP 11 DW1 flip-                       
                              flop in DCPP 11                             
                              (normal interrupt to                        
                              DCPP 11 from MPU 21).                       
                              (Note 2)                                    
__________________________________________________________________________
 Notes:                                                                   
  (1)If MIRO3 = 1, then set DCPP 11 clear flip-flop, otherwise reset it.  
 (2)DWI flip-flop will be set as a result of any DW · INST unless
 DCPP 11 clear flip-flop is set. Once DWI is set, it will remain set until
 tested by MPU 21, or until DCPP 11 clear flip-flop is set.               
 
    
     STATUS WORDS (DR·INST). 
     In addition to device address, the status word contains 4 bits placed on the external bus 57 (EXT1 -- 16): 
     Ext01: execption bit: This bit is set if either EXT02 or EXT03 is set. This bit is reset when a status read DR·INST) is executed. It is not reset with an enable status (ENST/). 
     Ext02: mpm23 parity error: This bit is set by a MPU 21 parity error and is reset by a status read or clear DCPP 11. When MPM 23 parity error is set, MPU 21 clock will be stopped. 
     Ext03: spm 39 parity error is set by an SPM 39 parity error and is reset by a clear DCPP 11. When SPM 39 parity is set, the MPU 21 clock will be stopped. 
     Ext04: run indicate status of DCPP 11. If set, indicates that DCPP 11 is executing instructions. If reset, indicates that DCPP 11 is stopped. This bit is used by MIR only. 
     Status interrupt: this level is set by an MPM 23 or SPM 39 parity error or by firmware control of MPU 21. It is reset upon a status read or clear DCPP 11. If status interrupt is set and the exception bit is not set a &#34;Soft Interrupt&#34; is indicated (normal completion of most operations). 
     DATA COMMUNICATIONS PREPROCESSOR LOGIC FUNCTIONS 
     The DCPP 11 includes the following logic (see FIG. 4): 
     A. function control register (FCR) 35 -- controls data path and functional operations within the DCPP 11. 
     B. adapter I/O register 61 -- used for exchange of data between MPU 21 and the data comm line adapters 19. 
     C. memory address register (MAR) 53 -- used to address memory for direct memory access (DMA) operations. 
     D. memory data register (MDR) 55 -- used for data storage for DMA read or write operations. 
     E. bit isolation unit (BIU) 63 -- used to select a particular bit of status or SPM information to be applied to the external interrupt input of MPU 21. 
     F. scratch pad memory (SPM) 39 -- used by MPU 21 for the storage of control information. 
     G. automatic operation logic -- used for the automatic transfer of 16 bits of information between SPM 39 and working registers. In some cases an index value may be added during the transfer. 
     H. adapter 19 -- multiple data comm line adapters may be contained in a single DCPP 11. The adapter 19 contains registers and logic as required to interface with data sets 17. 
     FUNCTION CONTROL REGISTER 35 (DEVO) 
     This register is loaded by an MPU 21 DEVO instruction. It controls the data path and logic functions of the DCPP 11 as shown in FIG. 5 and FIG. 6. 
     AUTOMATIC OPERATION 
     A very important feature of the present invention is the capability to automatically transfer two bytes of SPM data not using MPU 21. The starting byte address of the SPM 39 data is defined by a preceding MPU 21 DEVI instruction and must be an even-numbered address. The automatic transfer may include the addition of an index to the SPM 39 data. The index of one byte is contained in the adapter I/O register 61 and is added if the &#34;index&#34; bit is set. The results of the automatic function will be transferred to the register specified by the &#34;destination&#34; bits; also, if the &#34;SPM updata&#34; bit is set, the results will be stored into SPM 39 in place of the original data. When MAR 53 is the selected destination, a DMA operation to main memory 28 is initiated by requesting &#34;steal&#34; upon completion of the automatic transfer. Whether the memory operation is a read or a write is defined by the &#34;DMA write&#34; bit. The clock to MPU 21 will be stopped for the duration of the automatic operation and if a &#34;DMA read&#34; is initiated, the MPU 21 clock will not be restarted until the completion of the memory read operation. It is possible for an automatic operation to result in an overflow. In this case the &#34;auto overflow&#34; flip-flop is set for subsequent testing by MPU 21. The &#34;overflow&#34; flip-flop will not reset until the next &#34;AUTO OP&#34; is initiated. The function code calling forth an automatic operation is 100 in bits MD5-MD8 of a DEVO instruction. Functional descriptions of the automatic operation codes are given below. 
     
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AUTOMATIC OPERATION (FUNCTION CODE 100)                                   
(MSB)                  UP-                                                
INDEX DATA     DEST.   DATE                                               
(3)   WRITE    SELECT  SPM      DESTINATION                               
______________________________________                                    
1     1        0 0      0     Add index contained                         
                              in adapter I/O register                     
                              61 to 2 bytes of SPM                        
                              39 data. Load result                        
                              into MAR 53 and                             
                              initiate a DMA write                        
                              operation. (Note 1)                         
1     0        0 0      0     Same as above except                        
                              initiate a DMA read                         
                              operation. (Note 2)                         
1     1        0 0      1     Add index in adapter                        
                              I/O register 61 to                          
                              2 bytes of SPM 39                           
                              data. Store result                          
                              into SPM 39 in place                        
                              of original data and                        
                              also into MAR 53 and                        
                              initiate a DMA write                        
                              operation.                                  
1     0        0 0      1     Same as above except                        
                              initiate a DMA read                         
                              operation. (Notes                           
                              2 and 4)                                    
0     1        0 0      0     Transfer 2 bytes of                         
                              SPM data into MAR                           
                              and initiate a DMA                          
                              write operation.                            
0     0        0 0      0     Transfer 2 bytes of                         
                              SPM data into MAR 53                        
                              and initiate a DMA                          
                              read operation.                             
                              (Notes 2 and 4)                             
1     0        0 1      0     Add index in adapter                        
                              I/O register 61 to 2                        
                              bytes of SPM data;                          
                              store result into                           
                              MDR 55.                                     
1     0        1 0      0     Add index in adapter                        
                              I/O register to 2                           
                              bytes of SPM data;                          
                              store result into                           
                              CRC register 41.                            
1     0        0 1      1     Add index in adapter                        
                              I/O register 61 to 2                        
                              bytes of SPM data;                          
                              store result into MDR                       
                              register 55 and also                        
                              into SPM 39 in place                        
                              of original data.                           
1     0        1 0      1     Same as above except                        
                              CRC register 41 is                          
                              destination instead                         
                              of MDR 55.                                  
1     0        1 1      1     Add index in adapter                        
                              I/O register 61 to 2                        
                              bytes of SPM data.                          
                              Store result into SPM                       
                              39 in place of                              
                              original data.                              
0     0        0 1      0     Transfer two bytes of                       
                              SPM data into MDR 55.                       
0     0        1 0      0     Transfer 2 bytes of                         
                              SPM data into CRC                           
                              register 41.                                
1     0        1 1      0     Test for AOV.                               
______________________________________                                    
 Notes:                                                                   
 (1)Codes not shown are not applicable.                                   
 (2)Automatic operations require approximately 3.5 microseconds.          
 (3)Index = add contents of adapter I/O register 61 to least significant 8
 bits of AUTO OP; and all zeros to most significant 8 bits of AUTO OP.    
 Carries are propagated from LS through MS byte.                          
 (4)Data read from main memory 28 will be loaded into both MAR 53 and MDR 
 55.                                                                      
 
    
     
         ______________________________________                                    
MAR 53 AND MDR 55 SELECT (FUNCTION CODE 111)                              
A. MAR 53 SELECT                                                          
MD1   MD2             MD5                                                 
MSB   WT     MD3-4    IM-                                                 
MEM   OR     DEST =   MED-                                                
INH   DR/    MAR      IATE    DESCRIPTION                                 
______________________________________                                    
0     1      0 0      0     MAR 53 is enabled for                         
                            data exchange with MPU                        
                            21 via OUT2 or BEX2. A                        
                            DMA (main memory 28 write)                    
                            will follow second OUT2                       
                            and MPU 21 will be                            
                            stopped until the read                        
                            is complete (Note 3)                          
0     0      0 0      0     Same as above except a                        
                            DMA (main memory 28 read)                     
                            will follow second OUT2                       
                            and MPU 21 will be                            
                            stopped until read is                         
                            completed. Data will be                       
                            loaded into both MAR 53                       
                            and MDR 55.                                   
0     1      0 0      1     A DMA main memory 28                          
                            write will commence                           
                            immediately. Memory                           
                            address is as per                             
                            existing contents of                          
                            MAR 53.                                       
0     0      0 0      1     Same as above except                          
                            memory operation will                         
                            be a read and MPU 21                          
                            will be stopped until                         
                            read is completed. Data                       
                            will be loaded into both                      
                            MAR 53 and MDR 55.                            
1     0      0 0      0     MAR 53 is enabled for                         
                            data exchange with MPU                        
                            21 via OUT2 or BEX2.                          
                            DMA operation is disabled,                    
                            thus MAR 53 can be used                       
                            as a scratch pad data                         
                            register.                                     
______________________________________                                    
 Notes:                                                                   
 (1)Combinations not shown above are not applicable.                      
 (2)DMA operations use MAR for memory address and MDR 55 for memory data, 
 i.e., if memory operation is a read, MAR 53 and MDR 55 will be loaded wit
 data read from main memory 28. In the case of a memory write operation,  
 MDR 55 is previously loaded by MPU 21 with data to be written into main  
 memory 28.                                                               
 (3)MAR 53 is a 16-bit register. This requires two BEX2 or OUT2           
 instructions by MPU 21 for complete data transfer.                       
 
    
     
         ______________________________________                                    
B. MDR 55 SELECT                                                          
MD1                                                                       
(MSB)                                                                     
AUTO         MD3-4                                                        
SPM          REG.                                                         
LOAD  MD2    SELECT   MD5    DESCRIPTION                                  
______________________________________                                    
0     X      0 1      X    MDR 55 is enabled for data                     
                           exchange with MPU 21 via                       
                           OUT2 or BEX2 instruction.                      
1     0      0 1      0    Contents of MDR 55 will                        
                           be stored into two                             
                           consecutive bytes of SPM                       
                           39. Start address of                           
                           SPM 39 is specified by a                       
                           previous DEV1 instruction.                     
                           (Note 4)                                       
1     0      1 0      0    Same as above except CRC 41                    
                           register instead of MDR 55.                    
______________________________________                                    
 Notes:                                                                   
 (1)MDR 55 and CRC 41 are 16-bit registers and thus require two BEX2 or   
 OUT2 instructions to complete a data transfer.                           
 (2)MDR 55 is primarily intended for use as a data exchange register with 
 main memory 28. However, it can also be used by MPU 21 as a scratch pad  
 register.                                                                
 (3)CRC 41 is primarily intended for CRC computation but it can be used as
 a scratch pad register by MPU 21.                                        
 (4)Contents of the adapter I/O register 61 will be shifted into the least
 significant byte of MDR 55. The adapter I/O register 61 and the most     
 significant byte of MDR 55 will contain zeros. This feature provides a   
 path for MTR testing of the adapter I/O register 61.                     
 
    
     LINE ADAPTER 19 RECEIVE-TRANSMIT CONTROLS (FUNCTION CODE 011) 
     The following controls are used for adapter 19 receive and transmit data exchange and sync detection, break, and second stop bit control. 
     
         ______________________________________                                    
                        RTS                                               
                        DELAY                                             
MD1  MD2    MD3    MD4  MD5      DESCRIPTION                              
______________________________________                                    
0    0      0      0    0      Enable contents of                         
                               adapter 19 receiver to                     
                               adapter I/O register 61.                   
                               adapter I/O will be                        
                               loaded on a subsequent                     
                               BEX0.                                      
0    1      0      1    0      Same as above except                       
                               overrun status output of                   
                               selected adapter 19 will                   
                               be stored in the BIU 63.                   
                               (Note 1)                                   
0    0      0      0    1      Same as above but                          
                               adapter 19 receiver                        
                               logic will commence sync                   
                               detection.                                 
1    0      0      0    0      Transfer contents of                       
                               adapter I/O register 61                    
                               (previously loaded by an                   
                               OUT0 or DEV3) into the                     
                               transmit logic of                          
                               adapter 19.                                
1    1      0      1    0      Same as above except                       
                               underflow status output                    
                               of selected adapter 19                     
                               will be stored in the                      
                               BIU 63 (Note 1).                           
1    1      0      1    1      Enable the adapter 19                      
                               flip to receive mode.                      
1    0      1      0    0      Transmit logic is                          
                               directed to transmit                       
                               break character (all                       
                               spaces).                                   
______________________________________                                    
 Note:                                                                    
 (1)The stored data (overrun or underflow) should be tested on the next   
 instruction.                                                             
 
    
     REQUEST TO SEND DELAY BIT (MD5) 
     Another important feature of the present invention is the RTS dealy bit, which when sent, allows the transmitter logic to send one more character. This character is inhibited from being transmitted but is used as a delay for turning off the request to send (RTS) line. 
     In the asynchronous mode, the RTS delay time is one bit time plus the number of first &#34;0&#34; in the RTS delay character that was loaded into the transmitter logic; for example: 
     
         ______________________________________                                    
EX RTS delay character:                                                   
                   1 1 1 0 0 0 0 0                                        
                   (8-bit character)                                      
Delay time for turning off RTS is:                                        
                   1 bit + number of &#34;0&#34;.                                 
                   1 bit + 5 &#34;0&#34; = 6 bit                                  
                   Time delay to turn off bits.                           
______________________________________                                    
 
    
     In the synchronous mode, it is just the number of &#34;0&#34;. Using the above example, the RTS delay would be 5 bit times. 
     Notes: 
     (1) At the same time that the RTS delay ends, and in a half duplex mode, the data to the receiver logic is enabled. This allows the adapter 19 to flip from the XMIT mode to the RCV mode when the RTS delay time expires. 
     (2) A jumper is available on each adapter 19 for direct connect modes of operation. This allows the adapter 19 to flip to the RCV mode without waiting for the RTS delay time to expire. 
     
         ______________________________________                                    
SPM 39 PAGE SELECT OR SET CPU 13 STATUS INTER.                            
(FUNCTION CODE 010)                                                       
MD1  MD2    MD3      MD4  MD5                                             
______________________________________                                    
0    0      SPM 39        0     Preset page select                        
            Page                register (to 0, 1, 2,                     
            Select              or 3) as specified by                     
            (Note 1)            SPM page select bits.                     
1    0      0        0    0     Set status interrupt                      
                                flip-flop. Once set,                      
                                this FF will remain set                   
                                until a CPU 13 status                     
                                read. (Note 2)                            
______________________________________                                    
 Notes:                                                                   
 (1)SPM 39 organization provides up to 4 pages (32 bytes each) for each   
 line 15, selectable by these two bits.                                   
 (2)Status interrupt to CPU 13 may also be set by parity error from either
 SPM 39 or MPU 21.                                                        
 
    
     ADAPTER C/D, STATUS, &amp; LINE FREQ SELECT (FUNCTION CODE 101) 
     The following word formats are used for testing adapter 19 receive (RCV) status, testing adapter transmit (XMIT) status, loading the adapter control descriptor, or selecting line frequency, in the respective order. 
     
         ______________________________________                                    
MD1   MD2-4       MD5                                                     
______________________________________                                    
0     RCV status  0      Select receive status; do                        
      bit select         not enable other functions.                      
      (Note 1)                                                            
0     XMIT status 1      Select transmit status; do                       
      bit select         not enable other functions.                      
      (Note 1)                                                            
1     N·A·                                              
                  0      Load contents of adapter I/O                     
                         register 61 into adapter 19                      
                         adapter descriptor register.                     
1     N·A·                                              
                  1      Load most significant digit                      
                         of adapter I/O register 61                       
                         into adapter 19 frequency                        
                         select register.                                 
______________________________________                                    
 Notes:                                                                   
 (1)These 3 bits will select which status bit (0 through 7) will be applie
 to the MPU 21 EXT interrupt input.                                       
 (2)Refer to FIG. 5 for word format of transmit status, receive status,   
 line frequency select, and adapter descriptor control words.             
 
    
     
         ______________________________________                                    
LINE SELECT, DATA SET DESCR &amp; MGR STATUS                                  
(FUNCTION CODE 110)                                                       
MSB                                                                       
MD1   MD2-4     MD5                                                       
______________________________________                                    
0     S S S     1       Load contents of adapter I/O                      
      (Note 1)          register into line select                         
                        register.                                         
1     S S S     0       Load contents of adapter I/O                      
      (Note 1)          register into adapter data                        
                        set descriptor register.                          
0     S S S     0       Test selected bit of MGR                          
      (Note 1)          status without enabling                           
                        above functions.                                  
______________________________________                                    
 Note:                                                                    
 (1)SSS = Manager status bit select. MGR status testing is enabled at all 
 times. These 3 bits will select which status bit (0 thru 7) will be      
 applied to the MPU 21 external interrupt input (EXT).                    
 
    
     ADAPTER I/O REGISTER 61 
     This register, see FIG. 4, is used to exchange data between MPU 21 and the selected data comm line adapter 19. It is loaded by MPU 21 by an OUTO or DEV3 instruction, see FIG. 5. Once loaded, the contents of the adapter I/O register 61 can be transferred to any one of eight destinations by loading the appropriate command into the FCR (Function Control Register) 35 by an MPU 21 DEVO instruction. Receive data is read from the adapter 19 as follows: The FCR 35 is loaded (via a DEVO MPU 21 instruction) to select RCV data, then a one-instruction delay is required to allow access time. An MPU 21 BEXO instruction will now transfer the contents of the RCV logic data buffer to the MPU 21 B-register via the adapter I/O register 61. 
     Formats of the various data and control words handled by the adapter I/O register 61 are described in detail below with reference to FIG. 7. 
     
         ______________________________________                                    
DATA SET 17 DESCRIPTOR (See FIG. 7)                                       
BIT              FUNCTION                                                 
______________________________________                                    
Request To  If set, notifies the data nodem to go into                    
 Send (RTS) a transmit mode.                                              
Originate   If set, notifies the data modem to enter                      
 (ORIG)     the auto dial mode.                                           
Data        If set, notifies the data modem that the                      
 Terminal   business machine is ready. Also used in                       
 Ready (DTR)                                                              
            auto dial mode.                                               
Data Mode   If set, notifies the data modem that the                      
 (DMODE)    auto dial cycle has been completed.                           
New         If set, notifies the data modem that it                       
 Synchronous                                                              
            is at the hub station in multi-station                        
 (NEW SYNC) arrangements such as polling, to assure                       
            rapid synchronization between messages.                       
RATE        If set, notifies certain data modems to                       
            select a back-up rate (see standby rate).                     
STANDBY RATE                                                              
            If set, notifies certain data modems to                       
            select a back-up rate, as follows:                            
                  STANDBY                                                 
                  RATE       RATE                                         
          2400 Baud                                                       
                  0          0                                            
          1200 Baud                                                       
                  1          1                                            
           600 Baud                                                       
                  1          0                                            
2nd STOP BIT                                                              
            Used in asynchronous mode; if set, causes                     
            character transmitted to have two stop                        
            bits.                                                         
ENABLE XMIT These bits are used to enable the                             
and         transmitter and receive portions of the                       
ENABLE RCV  adapter 19.                                                   
            They are also used in half duples mode to                     
            disable the XMIT or RCV portion that is                       
            not being used, as follows:                                   
                    ENABLE    ENABLE                                      
                    XMIT      RCV                                         
          Full Duplex                                                     
                    1         1                                           
          Half Duplex                                                     
          (Transmitting)                                                  
                    1         0                                           
          Half Duplex                                                     
          (Receiving)                                                     
                    0         1                                           
          No Operation                                                    
                    0         0                                           
            If ENABLE XMIT is reset, the transmitter                      
            logic and line break function are held                        
            cleared. The data from the transmitter                        
            logic will be in a mark state                                 
            If ENABLE RCV is reset, the receiver                          
            logic and sync detection logic is held                        
            in a cleared state.                                           
TRANSMIT    If set, notifies the transmitter logic                        
 PARITY     to replace the trailing bit of character                      
            with a parity bit. If reset, no parity                        
            is transmitted and the last bit is                            
            treated as a data bit.                                        
CHARACTER   Notifies the DCPP 11 to transmit and/or                       
 SIZE       receive 5, 6, 7 or 8 bits, including                          
            parity and exclusing start and stop bits.                     
             CHAR SIZE  Y     X                                           
             5         1      1                                           
             6         1      0                                           
             7         0      1                                           
             8         0      0                                           
ASYNCHRONOUS                                                              
            If set, notifies the adapter 19 to                            
            operate in an asynchronous mode.                              
            If reset, the adapter 19 will operate                         
            in a synchronous mode.                                        
EVEN        If set, notifies the adapter 19 to                            
            transmit or receive even parity.                              
            If reset, notifies the adapter 19 to                          
            transmit or receive odd parity.                               
RCV PARITY  If set, notifies the adapter 19 that                          
            parity error will be enabled.                                 
            If reset, notifies the adapter 19 that                        
            parity error will be disabled.                                
            Also, if set and in synchronous mode,                         
            sync detection will be ASCII; if reset                        
            and in synchronous mode, sync detection                       
            will be EBCDIC.                                               
______________________________________                                    
 
    
     LINE FREQUENCY SELECTION (See FIG. 7) 
     Used to select baud rate for each line in asynchronous operations. During synchronous operations the respective line should be set to off. A separate frequency select register is provided for each line. The following listing defines the register content required for each frequency selection. 
     
         ______________________________________                                    
BIT PATTERN                                                               
2**3   2**2     2**1     2**0          MEANING                            
______________________________________                                    
0      0        0        0      =    OFF                                  
0      0        0        1      =     75 bits/sec                         
0      0        1        0      =     100 bits/sec                        
0      0        1        1      =     110 bits/sec                        
0      1        0        0      =     150 bits/sec                        
0      1        0        1      =     200 bits/sec                        
0      1        1        0      =     300 bits/sec                        
0      1        1        1      =     600 bits/sec                        
1      0        0        0      =    1200 bits/sec                        
1      0        0        1      =    1800 bits/sec                        
1      0        1        0      =    2400 bits/sec                        
1      0        1        1      =    4800 bits/sec                        
1      1        0        0      =    9600 bits/sec                        
1      1        0        1      =    19.2K bits/sec                       
1      1        1        0      =    N/A                                  
1      1        1        1      =    SPARE                                
______________________________________                                    
 
    
     STATUS WORDS AND BIT ISOLATION UNIT (BIU) 63 (FIG. 8) 
     The BIU 63, see FIG. 4, provides the capability to select one of up to eight bits in a status word and apply it to the EXT input of the MPU 21. 
     Status word selection and bit selection is accomplished by an MPU 21 DEVO instruction loading the appropriate command into the function control register 35. 
     SPM 39 BIT SELECTION 
     If SPM bit selection is desired, this is accomplished by an MPU 21 DEV1 instruction loading the appropriate command into the SPM address and control register 56. In this case the MPU 21 condition test operation (EXT TEST) must immediately follow the DEV1 instruction. The selected SPM bit will be applied to the MPU 21 EXT input for only one instruction period after execution of the DEV1 because EXT will revert back to the previously selected status bit. 
     
         __________________________________________________________________________
MGR STATUS                                                                
(See FIG. 8)                                                              
         BIT       FUNCTION                                               
(3)      Reset DWI Indicates a DWI has been received from                 
         (Device   the CPU 13. This usually indicates                     
         Write     that the CPU 13 wants to establish                     
         Instruction)                                                     
                   communications with MPU 21. The DWI                    
                   bit is reset upon selection by an                      
                   FCR command jand its previous state                    
                   is transferred to the EXT interrupt                    
                   flip-flop for subsequent testing by                    
                   MPU 21.                                                
(2)      AUTO OP ADV                                                      
                   Indicates that the last automatic                      
                   operation resulted in an adder overflow                
                   due to an index add function. This                     
                   flip-flop, once set, will remain set                   
                   until the next AUTO OP (either index                   
                   add or SPM load) is initiated. It is                   
                   always unconditionally reset at this                   
                   time.                                                  
(1)      TI (Timer This flag is set when the &#34;strobe                      
         Interrupt)                                                       
                   timer&#34; instruction is executed and                     
                   the one-millisecond timer had expired.                 
                   It is used by the MPU 21 program to                    
                   determine whether or not to increment                  
                   various timing delay counters associated               
                   with each adapter 19.                                  
(0)      DWI (Device                                                      
                   Indicates a DWI has been received from                 
         Write     the CPU 13. This bit is not reset                      
         Instruction)                                                     
                   when tested and remains set until a                    
                   reset DWI or a system clear is                         
                   performed.                                             
XMIT STATUS                                                               
(See FIG. 8)                                                              
(7)      XMIT      This flag is set if one or more of                     
         Exception the following conditions take place:                   
                   1. Clear to send is false.                             
                   2. Data set ready is false.                            
                   3. Break condition is true.                            
(6)      CTS (Clear                                                       
                   This flag is set if clear to send is                   
         To Send)  true. This flag is reset if clear to                   
                   send is false.                                         
(5)                (Not used.)                                            
(4)      DSR/ )DATA                                                       
                   This flag is set if data set ready                     
         Set Ready)                                                       
                   is false. This flag is reset of data                   
                   set ready is true.                                     
(3)      Break     This flag, if set, indicates the                       
                   receiver logic has detected a start                    
                   bit and the absence of a stop bit.                     
                   Used in asynchronous full-duplex                       
                   mode as a potential break indication.                  
(2)      Line/     This flag is set if the receive data                   
                   line is in a space condition. This                     
                   flag is reset if the receive data                      
                   line is in a mark condition (see note).                
(1)      LIne      This flag indicates that a line                        
         Change    change has occurred since the last                     
                   time this bit was tested. This flag                    
                   is reset when tested. It is set if                     
                   a mark to space or space to mark                       
                   change has occurred since it was                       
                   tested (see note).                                     
(0)      BMT       This flag is set if the transmitter                    
         (Buffer   logic can accept a new character. It                   
         Empty)    is reset when a transmit strobe has                    
                   been done to the selected adapter 19.                  
__________________________________________________________________________
 Note: The line/ and line change bits are used to accomplish monitor dial 
 response and break detection.                                            
 
    
     
         ______________________________________                                    
RCV STATUS (See FIG. 8)                                                   
BIT              FUNCTION                                                 
______________________________________                                    
(7)   RCV         This flag is set if one or more of                      
      Exception   the following conditions take place:                    
                  1. Parity error is true.                                
                  2. Data set ready is false.                             
                  3. Break condition is true.                             
                  4. Carrier lost is true.                                
(6)   PARITY      This flag is set if the character in                    
      ERROR       the receiver logic output buffer                        
                  register has bad parity. The bit will                   
                  be reset when the character is                          
                  transferred to the adapter I/O                          
                  register 61.                                            
(5)   CARRIER/    This flag is set if the data carrier                    
                  detect line is false. It is reset if                    
                  the data carrier detect line is true.                   
(4)   DSR/ (Data  This flag is set if data set ready is                   
      Set Ready)  false. It is reset if data set ready                    
                  is true.                                                
(3)   BREAK       This flag, if set, indicates the                        
                  receiver logic has detected a start                     
                  bit without an appropriate stop bit.                    
                  It is used in asynchronous mode and                     
                  is reset after testing.                                 
(2)   RING        This flag is set if the ring indicator                  
                  line is true. It is reset if the ring                   
                  indicator line is false.                                
(1)   CARRIER     This flag is set if the data carrier                    
      LOST        detect line goes true and then goes                     
                  false. It is reset when tested.                         
(0)   BFUL        This flag is set if the receiver                        
      (Buffer     logic has a full buffer. It is                          
      Full)       reset when the character is unloaded                    
                  by the DCPP 11 controller.                              
______________________________________                                    
 
    
     SPM 39 ADDRESS AND CONTROL 
     The scratch pad memory 39 is designed in the preferred embodiment to be expandable in blocks of 512 × 9. 
     The SPM 39 may be accessed in a character or bit mode operation. Bit mode can access one of 32 bits per page. Character mode can access all of the 32 bytes in a page including the 4 bytes used by bit mode. 
     SPM 39 organization provides for a maximum of four lines with up to four pages per line. Page addressing is accomplished by the FCR 35 via &#34;line select&#34; and &#34;page select&#34; commands. Line select will define a group of four pages and page select will define one of those four pages. The SPM address and control register is loaded via a DEV1 instruction (see FIG. 6 and FIG. 9) from MPU 21. 
     SPM ADDRESS AND CONTROL - DEV1 INSTRUCTION (FIG. 9) 
     CHAR or BIT/: Determines whether access will be character or bit mode. 
     Character mode will either: 
     1. Read the specified location into the SPM 39 I/O register which then may be read into MPU 21 via a BEX1 instruction. 
     2. Write the contents of the SPM I/O register into the specified location in the SPM 39. The SPM I/O register is previously loaded from MPU 21 may an OUT1 or OUT3 instruction. 
     3. If update is set, the specified address of SMP 39 is in the upper page. If update is reset, the specified address of SPM is defined by SPM page select. 
     Bit mode will either: 
     1. Read the specified location into the SPM I/O register and apply the selected bit 0 thru 7 to the EXT input of MPU 21. 
     2. set or reset the specified bit location in SPM 39. 
     SPECIAL CONSIDERATIONS 
     1. To access RCV data, wait one instruction, after the DEVO command before doing a BEXO to allow access time on the receive logic. 
     2. SPM bit access (BIU) correlates to character mode locations 28, 29, 30 and 31. 
     3. An SPM bit read must be tested on the following instruction by MPU 21. 
     4. MPM 23 parity or SPM 39 parity stop DCPP 11 can be reset with a clear only. 
     5. After a DMA operation, MDR 55 must be selected before addressing information. 
     DATA COMMUNICATIONS LINE ADAPTER 19 
     The data communications line adapter 19, see FIG. 4, includes the necessary logic to interface the DCPP 11 to a data communications network either by a data set 17 or by direct connect means. Thus the line adapter 19 provides the output interface of the DCPP 11. One line adapter 19 is required for each output line. In the preferred embodiment, the output line adaptor 19 is programmable to adapt to a variety of data set 17 requirements. In alternate embodiments, it is realized of course, that the line adapter 19 could be hardwired to provide the necessary interface between a specific set of data set 17 requirements and the DCPP 11. 
     The Line Adapter 19 includes the following functional blocks: 
     1. The Adapter Descriptor Register 69 which serves to define the functional operation of the Line Adapter 19. The Adapter Descriptor Register 69 is loaded from the Adapter I/O Register 61 and includes the following information bits (see FIG. 10) Receiver Parity Bit 75, Even Bit 77, Asynchronous Bit 79, Character (Y) Bit 81, Size (X) Bit 83, Transmitter Parity Bit 85, Enable Transmitter Logic Bit 87, and Enable Receiver Logic Bit 89. 
     2. Data Set Descriptor Register 91 which defines the functional operation of the specific data set 17 associated with a specific line adapter 19. The data set descriptor register 91 includes the following information bits (see FIG. 11): Second Stop Bit 93, Standby Rate Bit 95, Rate Bit 97, New Synchronization Bit 99, D Mode Bit 101, DTR Bit 103, ORIG BIT 105 and Request-To-Send Bit 107. The data set descriptor register 91 is loaded from the Adapter I/O Register 61. 
     3. The transmitter logic 109 which is a synchronous/asynchronous data communications adapter that accepts parallel binary data in the form of characters and serially transmits the data to a modem. Internally generated parity bit and appended control bits for asynchronous mode are transmitted at the same time if applicable. 
     4. The receiver logic 111 which is a synchronous/asynchronous data communications adapter for receiving serial digital data from a modem or other source. The receiver logic 111 organizes the received data into fixed word lengths corresponding to characters, and transmits these characters to a buffer register from which the character may be accessed in parallel format. 
     Each line adapter 19 also includes the following status registers: 
     1. The Receiver Status Logic 113 which provides the capability to select status information relative to receive mode and apply it to the bit isolation unit 63 for interrogation by the MPU 21. 
     2. The Transmitter Status Logic 115 which provides the capability to select status information relative to the transmit mode and apply it to the bit isolation unit 63 for interrogation by the MPU 21. 
     3. The Manager Status Logic 117 which provides data to the bit isolation unit 63 for interrogation by the MPU 21. Specifically, three bits of information are provided. The DWI Bit 119 which indicates that a device write instruction has been received from the CPU 13 which wants to communicate with the MPU 21. The DWI Bit 119 is reset by a reset DWI command 121 generated from the function control register 35. An AOV bit 123 indicates that an adder overflow occurred during the last automatic operation. The AOV bit 123 remains set until a subsequent automatic operation is initiated. A TI bit 125 is set when a strobe timer instruction is executed and a one millisecond time has expired. All bits from the Manager Status Logic 117 are presented to the bit isolation unit 63 for interrogation by the MPU 21. 
     Thus, the function of the line adapter 19 is to interface between the data sets 17 and the DCPP 11. In the preferred embodiment, as above described, the line adapter 19 is, in essence, microprogrammable and therefore universally applicable to a wide variety of output interface requirements. 
     Although an operative data communications preprocessor has been described it will be appreciated by those skilled in the art that modifications and additional features may be added without departing from the scope of the invention. As an example, provisions may be added for automatic dialing (AUTOCAL) and for cyclical redundancy checking (CRC). Furthermore, while the data communication preprocessing invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein.