Located cable wiring diagrams for cable from 3174 communications adapter to modem or other comm facility

DISCOVERED DIAGRAMS IN MAINTENANCE MANUAL SY27-2573-4 

On pages 2-102 to 2-104 there are diagrams of the wiring for the EIA (V.24/V.28 or RS232) cable, the X.21 cable and the V.35 cable. it shows the wiring, how the Oper/Test switch works, and even the differences in wiring for the wrap test plug that can installed instead of the cable.

FRU ID SYSTEM LESS SOPHISTICATED THAN I THOUGHT - MAYBE

Unless the microcode is doing some logical condition testing on the actual data and control signal lines, the only wires involved in the identification of the cable are CDID 6 (pin 14) and CDID 7 (pin 16) plus the signal ground line (pin 7).  One or both are connected to signal ground by the wiring in the connector, thus able to be sensed.

• CDID 7 only at ground is EIA/RS232
• CDID 6 only at ground is V.35
• CDID 6 and CDID 7 both at ground is X.21

The wrap plugs that can be installed have a different wiring of these signal lines. I am trying to find an unambiguous set of signals that the processor can check to choose which of the three cables and three wrap plugs are attached. 

The EIA wrap plug has pins CDID 6 and CDID 7 connected to each other (presumably not connected to signal ground). It also has the Test (pin 18) and Ring Indicator (pin 22) signals wrapped. 

The V.35 wrap plug has CDID 6 and CDID7 connected to each other and probably not to signal ground. Perhaps the lack of connectivity between 18 and 22 signals this is the V.35 versus EIA wrap plug. 

The X.21 wrap plug has CDID 7 tied to signal ground, with CDID 6 open. This looks like the EIA plug so some other set of connected pins must be sensed; those must not be used with EIA. Pins 9 and 13 are a good candidate as these don't exist in the EIA interface. 

DOCUMENTING THE WIRING AND CONNECTIONS 

I put together a handy spreadsheet showing all six wirings including the connections that occur inside the connector. I including three more that show the connections with one of the three cables when the Oper/Test switch is in test since this is slightly different from the wrap plug.

BUILDING WRAP TEST PLUG TO CHECK OUT THE CONTROLLER

I have some DB25 plugs onto which I can solder jumpers to create a wrap test plug. I will make the EIA one first as that is the mode I intend to use, but if I am bored and sitting there with spare DB 25 plugs . . . there may be others constructed.

VERIFICATION CHECKS NEEDED

The diagrams I have are ambiguous in some cases, therefore I have to test my presumed wrap connectors to see which version is properly identified by the microcode in the 3174. This will finalize the specs I have built.

My cable has two Oper/Test switches, thus I have to figure out how my cable compares to the three known cables and appropriately update the documentation.