[cctalk] Looking for Codex modem manuals/info

All – I’m working on a simulation project where I’m using two Codex 2121 LDSU (local data service unit) modems to simulate a leased line setup to a DECSYSTEM-2020. These modems use 2-pair cabling (TX+,TX-/RX+.RX-) and DCE DB25 connections. I believe each modem is working in loopback mode, but I can’t get it to work over the 2-pair interface between the modems (i.e., a loop back plug on one modem and terminal on the other). The only manual I’ve been able to locate is the sales brochure, not any kind of user manual. Anyway, have the interface cross-connected (i.e., TX to RX) but there are no polarity markings so I just used each pair in the same color order. Has anyone used this kind of modem before, have a manual, or know how to connect them? Thanks! Rich -- Rich Cini http://cini.classiccmp.org https://github.com/RichCini