Word processor
BACKGROUND OF THE INVENTION 
     The present invention relates to a word processor or text editor. Prior art devices of comparable function comprise automatic typewriters which allow editing of input data subsequent to playback. More specifically, the typist types in the data for printing and backspaces and types over to correct mistakes. Then, a button is depressed and the entire page is automatically printed or typed in corrected form. 
     Such an automatic typewriter, while allowing efficient correction of mistakes, suffers from several disadvantages. The page, while being initially typed, becomes cluttered and hard to read if there are a number of typeovers. This increases the possibility for error. It is not difficult to overlook a typographical error on a cluttered page and such an error requires correction and a second playback to produce an errorless copy. Another disadvantage of the typical automatic typewriter is slow operating speed. The typewriter may not be used to compose another page until the playback or printing of the first page is completed. 
     Another prior art device comprises a cathode ray tube which displays an entire page of printed characters. Subsequent to composing and correction of errors on the screen, that is, only after composition and correction of errors of the entire page, the entire page is printed. These systems suffer from the same drawback in that the display is inaccessible during printing. 
     Yet another drawback of such systems is that the display does not correspond to the printed page under some circumstances. In cases where the backspace and typeover functions, for example, are used to produce a Japanese Yen symbol ( ) by superimposing an equal sign (=) on the capital letter (Y), the position of subsequent data on the display does not correspond to the data as printed. This is because the printer has various control functions which are not provided to the display. 
     SUMMARY OF THE INVENTION 
     An advanced word processor which overcomes the above mentioned drawbacks of the prior art is disclosed in copending U.S. Patent application Ser. No. 841,830, filed Oct. 13, 1977, which is assigned to the same assignee as this application. The prior application discloses a CRT display unit which displays only one line of input data in addition to margin and similar position codes. After composition of the line, a printer prints out the line in response to a carriage return code or the like. The next line may be input and displayed while the first line is being printed. 
     The present invention constitutes a novel and unique improvement to the prior disclosure by providing means for setting the left margin to a new position. This is accomplished by depressing a left margin key on a keyboard followed by numerical keys indicating the new left margin position. Then, a carriage return key is depressed causing the new left margin position to be set into the display unit and printer. 
     It is a primary object of the present invention to provide an improved word processor comprising means for conveniently setting a left margin to a new position. 
     It is another object of the present invention to provide a word processor of increased operating speed compared to prior art apparatus. 
     It is another object of the present invention to provide a word processor comprising a CRT display which displays one line of characters and allows printing of one line while another line is being input. 
     It is another object of the present invention to provide a word processor which comprises a display unit on which characters are always displayed in the same positions as they appear after printing. 
     It is another object of the present invention to provide a word processor of increased efficiency at low manufacturing cost. 
     It is another object of the present invention to provide a generally improved word processor. 
     Other objects, together with the foregoing, are attained in the embodiment described in the following description and illustrated in the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a general block diagram of a word processor embodying the present invention; 
     FIG. 2 is a detailed block diagram of the word processor; 
     FIG. 3 is a flow chart of the operation of the word processor; 
     FIGS. 4 and 5 are tables illustrating the operation of the word processor; 
     FIG. 6 is a schematic diagram of part of the word processor; 
     FIGS. 7 to 9 are diagrams illustrating examples of character displays on a display unit of the word processor; 
     FIG. 10 is a graphic representation of a display function of the word processor; 
     FIGS. 11 and 12 are diagrams illustrating a left margin setting operation; and 
     FIGS. 13 to 15 are flowcharts of the operation of left margin setting means. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While the word processor of the invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodiment have been made, tested and used, and all have performed in an eminently satisfactory manner. 
     Referring now to FIG. 1 is the drawing, a word processor embodying the present invention is generally designated by the reference numeral 11 and comprises an input keyboard 12. Although not shown in detail, the keyboard 12 comprises a number of keys for inputting alphanumeric character data, symbols such as @, #, $, %, ¢, &amp; and *, and control codes such as backspace, carriage return and the like. Only a left margin key 12a is shown for simplicity of illustration. The output of the keyboard 12 is applied through an interface and buffer 13 and a control unit 14 to a memory 16. The control unit 14 feeds the data from the memory 16 through a cathode ray tube (CRT) interface 17 to a CRT display unit 18 which displays one line of data. The control unit 14 is constructed so that when a carriage return or line feed code is detected in the data from the memory 16, the line of data is fed to a printer 19 through a printer interface 21 and printed. The line of data is also fed through a floppy disc interface 22 to a floppy disc 23 for mass storage. The floppy disc 23 has the capacity to store many pages of character data and is constructed so that the data may be read therefrom and fed to the printer 19 to type entire pages automatically at any subsequent time. 
     In addition to the carriage return and line feed codes, the printer 19 will automatically print out the line of data when a hyphen (-) is detected in the data in a hot zone. Also, the printer 19 will print out the line of data when a space code is detected sufficiently close to the right margin and a character code is simultaneously detected in the right margin position. In this latter case, the next line of data displayed will begin with a data position following the space code. The apparatus 11 operates at optimum efficiency since the next line of input data is displayed on the display unit 18 while the previous line is being printed by the printer 19. The apparatus 11 is capable of various editing functions such as typeover, character insert and delete and the like although such is not the particular subject matter of the present invention and will not be described in detail. It is believed sufficient to state that the apparatus 11 provides the capability of perfectly composing the individual lines of data prior to printing. 
     Referring to FIG. 7, it will be seen that the present apparatus 11 also has the capability of displaying various marks above and below the line of data, FIG. 7 illustrating the appearance of a screen (not designated) of the display unit 18. It will be seen that left margin (LM), tabulation (tab), right margin (RM) and hot zone (HZ) marks are displayed above the line of data which is shown as being constituted by the alphabetic upper case characters (A), (B) and (C). The hot zone is constituted by a number of character positions to the left of the right margin which can be selected in accordance with the preference of the operator. Printing is effected if a hyphen or space code is detected in the hot zone. Also displayed below the line of data is a cursor which indicates the next position for data entry. 
     A detailed block diagram of the apparatus 11 is shown in FIG. 2. The data output from the keyboard 12 is fed to a keyboard decoder 24 which produces a number of control signal outputs for use by a general or overall control unit of the apparatus 11 which is not shown. The keyboard decoder 24 also decodes the data signals and stores the same in the memory 16. The output of the memory 16 is applied to a display decoder 26 which separates the alphanumeric and symbol codes from the control codes and passes the data for display to a display buffer 27 in a manner which will be described hereinbelow. The data is passed from the display buffer 27 to the CRT display 18. 
     In response to space (SP), hyphen (-), carriage return (CR), line feed (LF) or left margin (LM) codes the display decoder 26 feeds signals to set inputs of indicator flip-flops 28, 29, 31, 32 and 91 respectively. The space and hyphen codes are passed through AND gates 33 and 34 respectively. The Q outputs of the flip-flops 28, 29, 31, 32 and 91 are applied to inputs of an AND gate 36, the output of which is applied to a hyphenation alarm 37 such as a flashing light or buzzer. The Q output of a right margin indicator flip-flop 38 is also applied to an input of the AND gate 36. 
     A cursor or Y-address register 39, an end code or Z-address register 41, a starting or X-address register 42 and a current address register 43 are connected to the memory 16. In addition, the registers 41 and 42 are connected to the register 43. An up-down drive unit 44 is connected to the register 39 and an up drive unit 46 is connected to the register 43. 
     The apparatus 11 further comprises a register unit 47 which contains seven registers, each having the same number of bits as one line of data in the display buffer 27. The register unit 47 is connected to the CRT display 18 to control the display of the marks mentioned hereinabove and to provide other functions. The registers are not individually designated by reference numerals but are clearly labeled. 
     The registers are used for margin, tabulation, hot zone, flash (character highlighting by flashing), cursor, margin mask and line tail respectively. Outputs of the tab and line tail registers are connected to the display decoder 26. An output of the hot zone register is connected to inputs of the AND gates 33 and 34 as well as to an input of an AND gate 48. The space code output of the display decoder 26 is connected to another input of the AND gate 48. The output of the register 43 is connected to another input of the AND gate 48 and also to an input of a comparator 49. The output of the register 39 is connected to another input of the comparator 49, the output of which is connected to the cursor register of the register unit 47. The output of the comparator 49 is also fed to the set input of a read end indicator flip-flop 51, the Q output of which is connected to yet another input of the AND gate 36. 
     Another output of the display decoder 26 is connected to a drive input of an address pointer register 52 which controls the position of the data on the display. The register 52 is connected to the register unit 47. The output of the address pointer register 52 is connected to an input of a comparator 53 which receives another input from a right margin register 54. The output of the comparator 53 is connected to the set input of the flip-flop 38. 
     The output of the AND gate 48 is connected to an input of a space address register 56, the output of which is connected to an input of a comparator 57. The output of the register 43 is connected to the other input of the comparator 57. The output of a left margin register 58 is connected to the address pointer register 52. 
     The output of the comparator 57 is connected to an input of a multiplexer 59, as is an output of the memory 16. Print mode inputs from the general control unit (not shown) are applied to inputs of AND gate 61 and 62 which each are capable of producing at their outputs an end of transfer signal EOT. Other inputs of the AND gates 61 and 62 are connected to outputs of the comparators 57 and 49 respectively. 
     The output of the memory 16 is also connected to a hyphen decoder 63, the output of which is applied to an input of an AND gate 64. The Q output of the flip-flop 29 is connected to another input of the AND gate 64. The output of the AND gate 64 is connected to another input of the multiplexer 59. An external carriage return (CR) code may also be applied to the multiplexer from the general control unit. 
     The output of the multiplexer 59 is applied to a print buffer 66 and a print start decoder 67. The output of the print buffer 66 is connected to an input of a print control unit 68 which feeds output strobe signals back to the print buffer 66. The output of the print buffer 66 is also fed to an input of a print end decoder 69, the output of which is connected to the print control unit 68. The output of the print start decoder 67 is also connected to the print control unit 68. The print control unit 68 feeds the data signals to the printer 19 together with strobe signals and is responsive to a ready signal from the printer 19. The output of the address pointer register 52 is applied to the display buffer 27 to select the address therein. 
     In response to depression of the left margin (LM) key 12a, the keyboard decoder 24 feeds a signal to a comparator 92 to enable the same. The comparator 92 has inputs connected to outputs of the registers 39 and 42 and produces a high output when the X and Y addresses are the same. This high output is fed to the keyboard decoder 24. 
     The output of the memory 16, the Q output of the flip-flop 91 and the Q output of the flip-flop 31 are connected to inputs of an AND gate 93, the output of which is connected to an input of a new left margin address buffer register 94. The output of the register 94 in addition to the Q outputs of the flip-flops 91 and 31 are connected to inputs of an AND gate 96, the output of which is connected to an input of a code-to-binary converter 97. The output of the converter 97 is connected to the left margin register 58. The left margin register 58 is also connected to the print control unit 68. 
     The operation of the apparatus 11 will now be described with reference being made to the drawing, particularly FIG. 2. A flowchart of the operation is presented in FIG. 3 and graphs illustrating various logical functions are presented in FIGS. 4 and 5. 
     Basic Data Entry and Display 
     The address specified in the X-address register 42, which is the starting address or the first available address in the memory 16, is fed into the current address register 43. The memory 16 typically has the capacity to store between several lines and one page of data. At the same time, the status of the line feed indicator flip-flop 32 is sensed. If the flip-flop 32 is logically low, the left margin address specified in the left margin address register 58 is fed into the address pointer register 52. This sets the first character or data space on the display unit 18 to the left margin. If the flip-flop 32 is logically high, indicating that the previous operation was a line feed operation, the contents of the line tail register of the register unit 47 are fed into the address pointer register 52 for increment. This sets the first data space on the display unit 18 to the data space at which the cursor was positioned at the time the line feed operation was effected. 
     After positioning of the first data space on the display unit 18 is completed, the indicator flip-flops 28, 29, 31, 32, 38, 51 and 91 as well as the flash, cursor, margin mask and line tail registers of the register unit 47 are reset or closed. This latter operation will be referred hereinbelow as &#34;register clear&#34;, and will not be described in detail repetitiously. 
     When the operator of the apparatus 11 depresses a key on the keyboard 12, a data code indicating the desired alphanumeric character, symbol, or control function is entered into the memory 16 and the drive unit 44 increments the Y-address register 39. It will be understood that the Y-address register 39 can also be decremented by the unit 44 for editing or composing. The display buffer 27 is cleared prior to entry of the new data. The X address is set into the current address register 43 from the register 42 and the data in the X address is transferred to the display buffer 27. Thereafter, the unit 46 increments the current address register 43 to read data from successively higher data positions in the memory 16 in synchronism with incrementation of the address pointer register 52 to enable successively higher data positions in the display buffer 27. In this manner, the data in the memory 16 between the X and Y positions is transferred into the display buffer 27 and displayed on the display unit 18. 
     The transfer of data is terminated when the comparator 49 detects coincidence between the contents of the registers 39 and 43. The comparator 49 produces a logically high output which is fed to the cursor register of the register unit 47 to position the cursor at the position corresponding to the Y or current address in the memory 16. As long as alphanumeric data or symbols are input into the memory 16 and the right margin is not reached, the input operation described hereinabove is continued. After transfer to the display buffer 27 is completed, the data in the display buffer is continuously displayed on the display unit 18. 
     The output of the comparator 49 is also applied to the set input of the read end flip-flop 51 and sets the same. The Q output of the flip-flop 51 constitutes a read end signal which indicates that the reading of data from the memory 16 into the display buffer 27 is completed. In response to the read end signal the contents of the Z address register are fed into the current address register 43. An end code is stored at the Z address in the memory 16, and is decoded by the display decoder 26. In response, the transfer operation is terminated and the register clear operation is effected. For entry of subsequent alphanumeric data and symbols, the display decoder 26 increments the Y-address register 39 by means of the drive unit 44 and also the address pointer register 52 in response to decoding of an alphanumeric or symbol code. 
     Hyphenation Alarm at Right Margin 
     After a character or symbol is input and displayed at the position next to the right margin, the address pointer register 52 is incremented to the right margin position and the comparator 53 senses coincidence between the contents of the registers 52 and 54. As the flip-flop 51 was reset during this operation, the high Q output thereof enables the AND gate 36. It will be assumed that the flip-flops 28, 29, 31 and 32 are reset and the high Q outputs thereof also enable the AND gate 36. The high output of the comparator 53 sets the flip-flop 38 and the high Q output thereof is applied to the AND gate 36 so that the AND gate 36 produces a high output which is fed to the hyphenation alarm 37. 
     The hyphenation alarm 37 may be a flashing light, buzzer or the like and is energized to warn the operator that the right margin has been reached. The apparatus 11 is placed in standby awaiting action by the operator, which may be to press the carriage return key or edit the data. In the latter case, editing is necessary if the right margin was reached in the middle of a word. After the action is taken, the operator may press the hyphen key which will cause the printer 19 to print the line of data. 
     Carriage Return Operation 
     Depression of the carriage return key on the keyboard 12 will cause the line of data stored in the display buffer 27 to be printed in the following manner. The carriage return code is decoded by the display decoder 26 which sets the flip-flop 31. The low Q output of the flip-flop 31 is applied to the AND gate 36 to inhibit the hyphenation alarm 37. The general control unit detects the high Q output of the flip-flop 31 to initiate the printing operation. 
     The X address is transferred into the current address register 43 from the register 42 and the register 43 is incremented by the unit 46 to successively read the locations in the memory 16 from X to Y and transfer the data contained therein to the print buffer 66 through the multiplexer 59. In synchronism, input strobe signals are applied to the print buffer 66 to sequentially enable the data locations therein. The print mode signal is applied to the AND gate 62 to enable the same. The AND gate 62 produces the end of transfer signal EOT when the Y address is reached and the comparator 49 produces a high output. The EOT signal causes the display buffer 27 to be cleared in preparation for display of the next line of data and the contents of the current address register 43 to be transferred into the X-address register 42 to set the new X address equal to the old Y address. 
     Simultaneously the print start decoder 67 decodes the data and produces a print start signal in response to the carriage return code CR. This indicates that the entire line of data has been stored in the print buffer 66. The print control unit 68, in response to the print start signal, feeds output strobes to the print buffer 66 causing the data to be transferred from the print buffer 66 to the print control unit 68. The print control unit 68 receives a ready signal from the printer 19 when the printer 19 is free for operation. The print control unit 68 feeds the data and print strobes to the printer 19 causing the printer 19 to print the line of data stored in the print buffer 66. It will be noted that during this time the keyboard 12 and display unit 18 are free to input the next line of data. 
     The print end decoder 69 searches the data for the CR code and feeds a print end signal to the print control unit 68 in response thereto. The print end signal causes the printer 19 to terminate printing and return to standby in preparation for printing the next line. The printer 19 feeds the print ready signal to the print control unit 68 upon entering the standby condition. Also in response to the print end signal the print buffer 66 is cleared in preparation for the next line printing operation. The printer 19 effects a carriage return operation after printing the line of data. 
     Line Feed Operation 
     The line feed operation is similar to the carriage return operation except as will be described below. The print start and end decoders 67 and 69 respectively are responsive to the line feed code LF in the same manner as to the carriage return code CR. 
     The display decoder 26, in response to the LF code, sets the flip-flop 32. Although the Y-address register 39 is incremented, the address pointer register 52 is not incremented. The contents of the address pointer register 52 are fed into the line tail register of the register unit 47. The printing operation is then carried out in the same manner as in the carriage return operation. 
     As described in the basic data entry and display section hereinabove, for displaying the next line of data the status of the flip-flop 32 is read and the contents of the line tail register of the register unit 47 are fed into the address pointer register 52 rather than the left margin address so that the next line of display starts at the data position at which the line feed operation was initiated. 
     Hyphen in Hot Zone 
     A high signal is applied from the hot zone register of the register unit 47 to the AND gate 34 when the address in the address pointer register 52 is in the hot zone. This enables the AND gate 34. When a hypgen code is decoded by the display decoder 26, the flip-flop 29 is set and the high Q output thereof is applied to the AND gate 64. The printing operation is then initiated in the same manner as described above. 
     In response to the hyphen code transferred from the memory 16 to the multiplexer 59, the hyphen decoder 63 produces a signal which is gated through the AND gate 64 to the multiplexer 59. In response to this signal, the multiplexer 59 adds a CR code to the data following the hyphen code. This CR code is decoded by the decoders 67 and 69 to begin and end the printing operation respectively. 
     It will be noted that the printing operation in response to depression of the hyphen key on the keyboard 12 occurs only when the hyphen is in the hot zone. The length of the hot zone is selected so that if a hyphen is detected therein it is statistically unlikely that enough space remains for another word in the line. 
     Space Code in Hot Zone 
     When a space code is detected in the hot zone and the right margin has been reached it is statistically likely that the operator has attempted to input too much data in the line. In this case, the printing operation is automatically effected and the display of the next line is initiated at the data address in the memory following the space. Thus, the excessive data is displayed at the beginning of the next line. 
     In response to a space in the hot zone, the flip-flop 28 is set. The AND gate 48 is enabled by the hot zone register of the register unit 47 and also by the display decoder 26 in response to the space code. This allows the contents of the current address register 43, which correspond to the address of the space in the hot zone, to be stored in the space address register 56. If another space code is detected after the first space code, the address of the new space code will be stored in the space address register 56. In this manner, the address of the space nearest the right margin is stored in the space address register 56. 
     When the right margin is reached the flip-flop 38 is set by the comparator 53. The hyphenation alarm 37 is inhibited by the low Q output of the flip-flop 28 applied to the AND gate 36. 
     The general control unit, in response to setting of both flip-flops 28 and 38, applied the print mode signal to the AND gate 61 and initiates the printing operation. When the address in the current address register 43 equals the address in the space register 56 corresponding to the address of the space nearest the right margin in the hot zone, the comparator 57 produces a high output which is gated through the AND gate 61 as the EOT signal. The EOT signal is also applied to the multiplexer 59 causing the same to add a CR code to the data after the space code. The register 43 is incremented and the contents thereof transferred to the X-address register 43. Thus, the next line of display will begin at the data position following the space. 
     Set Left Margin 
     To set the left margin the operator first positions the cursor below the current left margin. Then he depresses the left margin key 12a. It is desirable to inhibit the operation of the left margin key 12a unless the cursor is below the current left margin. The comparator 92 provides this function. The comparator 92 is enabled to produce a high output when the left margin key 12a is depressed. However, the comparator 92 will only produce a high output when the X and Y addresses are equal, which only occurs when the cursor is in the left margin position. The high output of the comparator 92 enables a gate (not shown) in the keyboard decoder 24 which allows the left margin code to be gated therethrough to the memory 16. If the cursor is not in the left margin position, the comparator 92 does not produce a high output and no operation will occur when the left margin key 12a is depressed. This operation is illustrated in the flow chart of FIG. 14. 
     Assuming that the cursor is in the left margin position depression of the left margin key 12a causes the left margin code to be stored in the X address in the memory 16. 
     Then, the registers 39 and 52 are incremented and the contents of the memory 16 (in this case only the left margin code) are transferred to the display buffer 27 through the display decoder 26. The display decoder 26 produces an output in response to the left margin code to set the flip-flop 91. The low output of the flip-flop 91 inhibits the hyphenation alarm 37 through the AND gate 36. 
     In the examplary case of FIGS. 11 and 12, the left margin is currently at space 10 and it is desired to reset the left margin to space 15. Thus, the operator depresses the left margin key and a left margin set symbol   is displayed at space 10. Then, the operator depresses keys on the keyboard 12 indicating the numerical address or space number of the new desired left margin position, in this case 15. The registers 39 and 52 are incremented in the manner described above and the digits 15 are displayed on the display 18 and stored in the memory 16. 
     Then, the operator depresses the carriage return key to produce the CR code which is stored in the memory 16 following the left margin code LM and the new left margin address code 15. In this case, the display decoder 26 produces a high output to set the flip-flop 31. 
     In response to the CR code, the general control unit executes the operations illustrated in FIG. 13. First, the address in the X address register 42 is transferred into the current address register 43. Then, the buffer register 94 is cleared. Next, the current address register 43 is incremented by means of the unit 46. In this manner, the first address in the memory 16 from which data is read out is the address of the first digit of the new left margin address code. Data is read out of the memory 16 and transferred into the buffer register 94 until the CR code is detected. At this time, the new address code is converted into a binary code by the converter 97 and transferred into the left margin register 58. The AND gate 93 prevents reading into the register 94 except when the flip-flop 91 is set and the flip-flop 31 is reset. When the CR code is detected and the flip-flop 31 set, the AND gate 93 is inhibited and the AND gate 96 is enabled to allow transfer of data from the register 94 to the converter 97. 
     The new left margin address code stored in the register 94 is typically in the ASCII format and must be converted to a pure binary number prior to being fed into the left margin address register 58. The converter 97 performs this function. After conversion, the new left margin address, in pure binary form, is transferred into the left margin address register 58. Then, the previous left margin bit in the margin register of the register unit 47 is reset and the bit corresponding to the new left margin address or position is set into the margin register. 
     Subsequently, the left margin code, new left margin address code and CR code are fed from the memory 16 into the print buffer 66 in the manner described above. Upon detection of the CR code by the print start decoder 67, the general control unit is controlled to start a print operation. However, prior to the print operation the register 43 is incremented and the contents thereof set into the register 42 in preparation for input of a new line of data. 
     The print sequence is shown in FIG. 15. If the flip-flop 91 were not set, the data in the print buffer 66 would be printed in the manner described above. However, since the flip-flop 91 is set, the general control unit does not cause data to be transferred from the print buffer 66 to the print control unit 68 but instead feeds a left margin signal to the print control unit 68. Then, the new left margin address is fed from the left margin register 58 into the print control unit 68. In response, the print control unit 68 inhibits feeding of output strobe pulses to the print buffer 66 and thereby inhibits printing. However, the print control unit 68 feeds the new left margin address into the printer 19 to internally set the left margin to the left margin address. Upon initiation of input of the next line of data, the new left margin address is transferred into the address pointer register 52, and the display 18 and printer 19 positioned at the new left margin address. Since the margin register of the register unit 47 was set to the new left margin address, the left margin mark will appear thereabove. FIG. 11 illustrates the appearance of the display 18 just before depressing the carriage return key and 12 illustrates the appearance thereafter. 
     FIG. 6 shows on exemplary embodiment of the display decoder 26 as comprising a decoder matrix 71. The alphanumeric (A/N) data, space (SP), hyphen (-) and left margin (LM) code outputs of the matrix 71 are applied to non-inverting inputs of an OR gate 72. TAB, CR, LF, half line feed (HLF), half reverse line feed (HRLF), margin release (MR), END and backspace (BSP) code outputs are applied to inverting inputs of the OR gate 72 respectively. The output of the OR gate 72 is applied to an AND gate 73 which receives strobe signals at another input thereof. The output of the AND gate 73 is applied to an UP drive input of an up-down drive unit 74. 
     The BSP code output of the matrix 71 and the strobe signals are applied to inputs of an AND gate 76, the output of which is applied to a DOWN drive input of the unit 74. 
     The TAB code output of the matrix 71 and the Q output of the line feed indicator flip-flop 32 are applied to inputs of an OR gate 77, the output of which is applied to a set input of a flip-flop 78. The Q output of the flip-flop 78 and the output of a clock pulse generator 81 are applied to inputs of an AND gate 79, the output of which is applied to another up drive input of the unit 74. Outputs of the tab and line tail registers of the register unit 47 are applied to inputs of an OR gate 82, the output of which is applied to the reset input of the flip-flop 78. The inputs to the OR gate 82 indicate that the tabulation or line tail position respectively has been reached. 
     In operation, each time a data code is entered from the keyboard 12 a strobe signal is fed to the AND gates 73 and 76. When the code is A/N, SP, - or LM a signal is gated from the matrix 71 through the OR gate 72 to the AND gate 73 in synchronism with the strobe signal. Thus, the AND gate 73 produces a signal which is applied to the unit 74 causing the same to feed a signal to the address pointer register 52 which causes the register 52 to increment. All other codes inhibit the AND gate 73. The BSP code is applied to the AND gate 76 which produces a high output in response to a backspace code. This is applied to the unit 74 which feeds a signal to the register 52 causing the same to decrement. 
     The unit 74 is also used to slew the address pointer register 52 for tabulation and line feed operations. The flip-flop 78 is set in response to either a TAB code from the matrix 71 or a high Q signal from the flip-flop 32. The resulting high Q output of the flip-flop 78 enables the AND gate 79 so that clock pulses from the generator 81 are applied to the unit 74. The unit 74 causes the register 52 to increment in response to each clock pulse. The flip-flop 78 is reset thereby inhibiting the AND gate 79 when either the tabulation point or the line tail is reached depending on whether the operation is tabulation or line feed. The CR, LF, SP, -, LM and A/N operations are summarized in FIG. 4 and the operation of the display decoder 26 is summarized in FIG. 5. 
     As mentioned hereinabove, it is desirable to display control codes in addition to character and symbol codes and further to maintain the display positions identical to the printing positions. Whereas prior art apparatus display control codes mixed with the character codes, the control codes displace the character codes rightwardly so that the position on a particular character on the display is rightward of the same character as printed. 
     FIG. 8 shows an example of such a display. In this case, the characters A, B and C are input and the tab key depressed. The cursor is moved to the first tabulation point and a rightwardly pointing arrow, indicating tabulation, is displayed in the space next to the character C. 
     FIG. 9 illustrates a case in which the characters A through F are input and the carriage return key is depressed. This initiates the printing operation. The cursor is not moved rightwardly as described above but a leftwardly pointing arrow indicating carriage return is displayed in the space next to the character F above the cursor before the display is cleared. 
     FIG. 10 shows the operation of the apparatus 11 in displaying (ABC 1,000). The Japanese Yen sign () is made by typing an equal sign (=) over the capital letter (Y). The operations of typing ABC followed by tabulation correspond to FIG. 8. Subsequently, the letter Y is input followed by a backspace (BSP). The cursor is moved back under the letter Y and a backspace mark () is displayed to the right of the letter Y. Next, an equal sign (=) is input to complete the symbol  . However, only the last entered data in the position of the letter Y, in this case the symbol =, is displayed. The cursor is moved rightwardly by one data space. As illustrated, a space (SP) code is then entered which moves the cursor rightwardly by one more position. Finally, 1,000 is entered. The final display is ABC=1,000 although the printed output will be ABC   1,000. 
     It will be seen that although it is possible to display only one character or symbol at a particular data position on the display, the positions of all data on the display correspond to the positions as printed. For each data position, where a typeover is accomplished to produce a composite symbol, the last entered data will be displayed. This makes it much easier to accurately compose the data on the display. 
     In summary, it will be seen that the present invention provides a word processor which operates at substantially improved speed and efficiency compared to the prior art. In addition, the data positions on the display correspond to data positions as printed, even if composite characters are produced by typeover operations. A novel and unique improvement to the word processor allows the left margin to be set to a new position merely by depressing a left margin key, followed by numerical keys indicating the new left margin space number or address and finally a carriage return key. Naturally, the particular configuration may be modified in such a manner that the last key to be depressed is some key other than the carriage return key. Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof. For example, the general principles of the invention may be used to set a right margin in addition to a left margin.