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RS232 Communications Cable for UMAC TurboPmac2 10 Pin IDC Header


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After struggling to duplicate a working cable that we had for the auxiliary serial port when we upgraded an old UMAC TurboPmac2 CPU to a newer style one, I thought I would document what actually is needed to generate the cable, and what needs to be done in order for it to work.


I started out with a 10 pin plug that matched the header, an IDC D9 Female connector, and a length of 10 conductor ribbon cable long enough to reach the computer that was controlling the PMAC. In the UMAC Turbo CPU HRM, there is a description of the two serial ports, detailing the usage of each pin, with a comment not to connect pin 1 if used for RS-232 communications. What was not said is that you do not connect pin 10, either, so that in effect, you only need 8 conductors for the cable. The figure showing the pinout from the HRM is duplicated here.



To make the cable, attach the ribbon cable to the 10 pin IDC connector, paying attention that the connector pin 1 is on the correct side of the cable. From the far end of the cable, strip back conductor 10 to the IDC plug, and cut the wire off. Also at the far end, separate conductor 1 from the cable, and peel it back about 1 inch (25 mm), and trim it off there. Now place the cable in the D9 IDC connector, aligning the cable such that the 8 remaining conductors fill positions 2-9, as shown in the following photos.



D9 connector opened up to show missing wire for pin 1



IDC10 plug shown plugged into main serial port of UMAC CPU. Note Brown wire that is trimmed close to the plug.


I hope that this post helps someone to avoid the frustration that I experienced learning what works with this cable.

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