the subject matter described herein provides improved methods and systems for providing diagnostic card management connectivity to a plurality of application cards in a shelf assembly using a shared serial management interface . the shared serial management interface may be provided on a shelf management card and may be accessible to an external manager . the shelf management card interacts with an application card at a level that does not require the operating system on the card to be operational . for example , the management card may provide diagnostic and management connectivity to the application cards during boot up and during or after an operating system failure . fig2 is a block diagram of a shelf assembly having a shared serial management interface in accordance with an aspect of the subject matter described herein . shelf management card 200 includes one or more external management ports 202 a , 202 b , and 202 c that may be used to interface with an external manager , a corresponding number of universal asynchronous receiver transmitters ( uarts ) 204 a , 204 b , and 204 c , a shelf management control processor 206 , a shelf management interface 208 , multiplexer and selector logic 210 , a rack control interface 212 , and a shared serial bus interface 214 . in fig2 , three external management ports 202 a , 202 b , and 202 c are shown . external management ports 202 a and 202 c may provide a direct terminal interface , while external management port 202 b may provide connectivity through a dedicated modem . each external management port 202 a , 202 b , and 202 c may interface with a respective uart 204 a , 204 b , and 204 c and may include circuitry needed to convert the interface signals to a format and level compatible with the uarts 204 a , 204 b , and 204 c . for example , external management ports 202 a and 202 c may include circuitry to convert the terminal interface signals from one voltage level , such as that used by serial interface standards such as eia / tia - 232 , to a voltage level compatible with the corresponding uart 204 a and 204 c . similarly , external management port 202 b may include circuitry , such as a modulator / demodulator , to convert encoded data received from the public switched telephone network ( pstn ) to a serial bit stream . uarts 204 a , 204 b , and 204 c interface with the shelf management processor 206 . as is known to the art , a uart receives data from a host processor and converts the data into a serial bit stream having a format that is compatible with a target serial device , such as a terminal . for example , the uart may add start , stop , and parity bits to each character and transmit the character to the terminal at a specified serial data rate . likewise , serial data that is received at a specified serial data rate from the terminal is converted by the uart into a suitable format by removing the start , stop , and parity bits . the uart may employ common flow control techniques and an internal data buffer to provide efficient communication between the shelf management control processor 206 and the external manager . as shown in fig2 , uarts 204 a , 204 b , and 204 c may be integral to shelf management processor 206 or may be peripheral to shelf management processor 206 and interface with shelf management processor 206 using conventional techniques , such as connection by an address and data bus . shelf management processor 206 provides a communication and control interface between an external manager and application cards in the shelf . shelf management processor 206 may receive a request from an external manager to connect to a particular application card in the shelf assembly . a connection menu generated by shelf management processor 206 may be viewed by the external manager and the connection request may be transmitted to shelf management processor 206 as a menu option selection . the connection menu may include a list of available ports that may be used to establish a connection and may be presented in a source - target format . for example , external management port 202 a , 202 b , or 202 c may be designated as a source port and either rack control interface 212 or shared serial bus interface 214 may be designated as a target port . the connection menu may list each possible source - target combination , or may utilize a two - step approach , with a source port identified in one step and a target port identified in another step . shelf management processor 206 may also be capable of receiving connection requests from a command line using a predetermined command format . after receiving a connection request , shelf management processor 206 may determine if the shelf resources needed to complete the connection ( i . e ., the designated source port and the designated target port ) are available . if shelf management processor 206 determines that connection resources are available , shelf management processor 206 may instruct the appropriate application card to attach to a shared serial bus 402 , for example by sending a connection command over shelf management interface 208 . shelf management interface 208 may be adapted to connect to management channel 404 . shelf management interface 208 may be implemented using a commercially available chip set , such as intel &# 39 ; s intelligent platform management interface ( ipmi ). ipmi , which is based on the inter - integrated circuit ( i 2 c ) bus developed by philips semiconductors , uses a serial data line and a serial clock line to support communication on management channel 404 . shelf management processor 206 may complete the connection between the appropriate external management port 202 a , 202 b , or 202 c and shared serial bus interface 214 using multiplexer and selector logic 210 . in addition to connecting to a local application card via shared serial bus interface 214 , a connection to a shelf manager controller 200 on an adjacent shelf may be established using rack control interface 212 . rack control interface 212 may be connected to a management port 202 a , 202 c on a shelf management controller 200 residing on an adjacent shelf using an external cable . once the connection between external management port 202 a , 202 b , or 202 c , and the target interface ( i . e ., serial bus interface 214 or rack control interface 212 ) is established , shelf management processor 206 monitors communications from the external manager to determine when to terminate the connection between the external manager and the target interface . the external manager may initiate the termination of the connection using an in - band command , such as a predetermined escape sequence , by changing the status of one or more hardware interface signals , or both . fig2 illustrates two application cards 300 , each of which may be identically configured to busses 402 and 404 . for simplicity , the internal components of one of the application cards are omitted from fig2 . in fig2 , application card 300 may include an application processor 302 , a shelf management interface 304 , a uart 306 , a shared serial bus interface 308 , and control logic 310 . application processor 302 may perform predetermined application functions , such as providing connection and management functions in a telecommunications network . application processor 302 may also respond to queries through shelf management interface 304 , which performs functions complementary to shelf management interface 208 . shelf management interface 304 may communicate with shelf management interface 208 on shelf manager controller 200 , including receiving and responding to various status messages . shelf management interface 304 may be implemented using a commercially available chip set , such as intel &# 39 ; s intelligent platform management interface ( ipmi ), and may include a dedicated management controller and interface logic . by using a dedicated management interface , such as ipmi , application processor 302 may be freed from responding to shelf - level management messages . in addition , in the event that application processor 302 ceases to function properly , access to the management functions of application card 300 may still be provided through shelf management interface 304 . uart 306 and shared serial bus interface 308 provide communication capability between application processor 302 and shared serial bus 402 . control logic 310 receives appropriate instructions from shelf management interface 304 to engage or disengage shared serial bus interface 308 from shared serial bus 402 . data received from shared serial bus 402 is reformatted by uart 306 and read by application processor 302 in due course . in accordance with one embodiment of the subject matter described herein , shelf management card 200 communicates with an application card 300 using a shared serial bus 402 . each application card 300 in a shelf may be connected to shared serial bus 402 . shelf management card 200 and application cards 300 may be configured in a master - slave configuration , with shelf management card 200 acting as the serial bus master . fig3 is a block diagram of an exemplary interface for a shared serial bus in accordance with an embodiment of the subject matter described herein . in fig3 , each redundant shared serial bus 402 a and 402 b may be implemented as a balanced , multi - drop transmission line , such as that defined by eia rs - 422 or rs - 485 . shelf management card 200 a or 200 b and each application card 300 a and 300 b may have a differential transceiver circuit 308 to interface to shared serial bus 402 a and 402 b . the receiver portion of transceiver circuit 308 of each application card 300 a and 300 b is connected to the transmitter portion of transceiver circuit 214 of shelf management card 200 a and 200 b . likewise , the transmitter portion of transceiver circuit 308 of each application card 300 a and 300 b is connected to the receiver portion of transceiver circuit 214 of the respective shelf management card 200 a and 200 b . each application card 300 a and 300 b may include provisions to ensure that only one application card is transmitting at a time to prevent bus contention . each application card 300 a and 300 b may include two serial ports for low - level diagnostics , with each serial part being supported by a uart 306 . one port may be a diagnostics port and the other may be a console port . the diagnostics port may provide access to diagnostics that are typically used during manufacturing test and may include the ability to access chip - level registers . the console port may provide access to higher - level functions and may be used to set initialization parameters . it is generally not necessary for the operating system to be functioning in order to utilize the console port . the application card 300 a and 300 b may access the diagnostic port and console port using separate transceivers , or a multiplexer may be used to select the port being connected to the bus 402 a and 402 b . each port may support diagnostic and console port functions , thereby providing dual functionality . as previously noted , only one application card 300 a or 300 b should transmit on each shared serial bus 402 a and 402 b at a time . shelf management card 200 a or 200 b may instruct the appropriate application card 300 a or 300 b to transmit on the bus by transmitting a command that includes the identity the target application card 300 a or 300 b . the command may be transmitted on shared serial bus 402 a or 402 b and the application card identity may be based on the slot location of the application card 300 a or 300 b . for example , a unique slot id may be hard - coded into a midplane connector at each slot location , thereby permitting application card 300 a or 300 b to determine its slot location in the shelf , even if application card 300 a or 300 b has limited functionality . since the receiver portion of transceiver 308 of each application card 300 a and 300 b can simultaneously access each shared serial bus 402 a and 402 b , a command sent by the shelf manager card 200 a or 200 b may be received by each application card 300 a and 300 b . each application card 300 a and 300 b may process the command to determine the intended destination address and ignore the command if it is addressed to another card . the shelf assembly may also provide a separate management channel 404 a and 404 b for routing command messages and performing other management functions . management channel 404 a and 404 b may be implemented using an ipmi architecture . the ipmi architecture includes a serial data signal and a serial clock signal . a bus master provides the clock signal , although ipmi supports multiple bus masters . thus , any ipmi interface on an ipmi bus may act as a master to initiate communication with another ipmi interface . the ipmi architecture may also include a dedicated controller 304 for receiving and processing management commands . using a dedicated controller 304 to process management commands rather than routing the management commands to application processor 302 provides increased reliability , since management commands can be received and processed even if application processor 302 is not functioning properly . moreover , the ipmi controller may provide additional services , such as reporting an application processor failure to shelf manager 200 a or 200 b using management channel 404 a and 404 b . fig4 is a block diagram of a midplane of a picmg 3 . 0 compatible shelf assembly including a shared serial bus for external diagnostics and console connections in accordance with an embodiment of the subject matter described herein . while the invention is described with reference to a picmg 3 . 0 compatible shelf , it should be appreciated that the description of the invention as set forth herein may be applied to other equipment shelf systems . accordingly , the invention should not be limited to any particular shelf architecture . referring to fig4 , the shelf assembly provides seventeen card slots arranged in parallel along the midplane . shelf assemblies typically provide a card slot for a shelf controller and the remaining sixteen slots are available for user devices . the picmg standard provides for redundant shelf management controller ( shmc ) cards 200 a and 200 b having a management interface to each card slot in the shelf . the shmc card defined by picmg is a half - height card , thus both shmc cards may reside in portions of the same physical slot thereby providing redundancy without reducing the number of available application card slots . as previously noted , the midplane supports the connectivity for zone 1 and zone 2 . zone 1 provides access to a power bus 503 and supports an interface to a management channel 505 from the shmc to each slot . the power bus 503 may provide access from each slot to at least one power supply . the management channel 404 may be used by various cards in a shelf to obtain initialization information and to conduct management functions , such as card diagnostics . each card in the shelf may include an intelligent platform management controller ( ipmc ) that communicates with the shmc . zone 1 may also provide a shelf address 507 , which may be used in conjunction with other information to identify and / or assign a unique address to each application card in a multi - shelf system . zone 2 supports clock and / or data transport across four separate interfaces . these interfaces include a base interface 509 , a fabric interface 511 , an update channel interface 513 , and a synchronization clock interface 515 . base interface 509 may support 10 / 100 / 1000base - t ethernet connections between application cards in a shelf . each application node slot may have a single , point - to - point base channel connection to each of two base hub slots 517 a and 517 b . base interface 509 may also support other ethernet - based services , such as tekelec &# 39 ; s proprietary imt management bus supported by imt hub cards 519 a and 519 b . fabric interface 511 supports non - ethernet - based communication between cards . redundant fabric interface cards 521 a and 521 b may be provided in the shelf assembly . each fabric interface card may include configuration information for application cards residing in the remaining card slots , and facilitate non - ethernet - based communication between application cards . as shown in fig4 , redundant fabric interface cards 521 a and 521 b reside in slot 7 and slot 8 . it should be appreciated that non - picmg compatible shelf architectures may not require the use of fabric interface cards , thus making these slots available for use by application cards . update channel interface 513 provides differential signal pairs for communication between slots . the signal pairs may be configured for point - to - point communication between two slots , with a card in one slot transmitting on a first signal pair and the other card transmitting on a second signal pair . in embodiments of the subject matter described herein , one card , such as the shmc , may be designated as the bus master and the signal pairs may be designated as a transmit pair and a receive pair with respect to the bus master . it should be appreciated that a card other than the shmc may act as the bus master . for example , if two application cards are communicating using update channel interface 513 , one card may be designated the master and an externally accessible console port on the master application card may be used to interface with the other application card . the shmc may communicate this designation to the application card using management channel 404 . it will be understood that various details of the invention may be changed without departing from the scope of the invention . furthermore , the foregoing description is for the purpose of illustration only , and not for the purpose of limitation , as the invention is defined by the claims as set forth hereinafter .