Multiplexing a ground signal on a high speed cable interface to provide access to cable vital product data

A logic card to which a cable is connectable, the logic card comprising:

• interface circuitry;
• a selected line to a non-volatile memory of a cable connectable to the interface circuitry to couple the logic card to an external device, the non-volatile memory storing cable vital product data (VPD);
• a switch having a first terminal coupled to the selected line, a second terminal coupled to a ground, and a control terminal;
• and
• a management controller having an output coupled to the control terminal of the switch and operable to:
• cause the switch to be in a first state in which the selected line is effectively coupled to the ground during normal operation of the external device;
• cause the switch to be in a second state when the management controller detects that the cable is connected to the interface whereby the selected line is decoupled from the ground and the cable VPD is accessible to the controller;
• adjust the interface circuitry in response to the cable VPD;
• and
• cause the switch to return to the first state after the management controller has accessed the cable VPD whereby the selected line is effectively coupled to the ground.

A computer program product of a computer readable storage medium usable with a programmable computer, the computer program product having computer-readable code embodied therein for accessing cable vital product data (VPD), the computer-readable code comprising instructions for:

• detecting the presence of a cable connected through interface circuitry to a logic card and coupling the logic card to an external device, the cable including a non-volatile memory storing cable VPD and having a selected line from the non-volatile memory to the logic card which is coupled to ground during normal operation of the external device;
• disconnecting the selected line from ground in response to detection of the cable;
• reading the cable VPD over the line from the non-volatile memory;
• reconnecting the selected line to ground;
• and
• tuning the interface circuitry in response to the cable VPD
• wherein the instructions for reading the cable VPD comprise instructions for reading a length of the connected cable and instructions for tuning the interface circuitry comprise instructions for adjusting amplification of signals being transmitted on the connected cable.