[mdlug] Semi-OT: Serial modem behavior

[Ingles, Raymond]

I have access to three serial modems, all different models. One of them works just fine - a USR Sportster. The other two (a Zoom 2400 baud, and another 14.4 modem whose manufacturer escapes me for the moment) display the same problem - no data coming back from the modem to the computer.

Cabling doesn't seem to be the issue; the same cables work with one modem, but not the other two. I've used a couple different cables, and used both USB-to-serial adapters and on-motherboard serial ports.

The behavior on the two problem modems is the same. Using a program like 'minicom' or 'gtkterm', I can see the modem notice things like DTR and such - the appropriate lights turn on. When I send AT commands, I can see the RD and even SD lights blink. Yet absolutely no response shows up in the terminal. On the working modem, I get responses without issue. But on the failing ones, nada.

I've tried bauds from 300 to 115200. (At higher bauds, the non-working modems RD and SD lights stop blinking.) I've pretty much stuck with 8N1 parity, but if anyone has suggestions for alternatives there I'm curious.

Obviously the use cases for serial modems are... pretty rare these days. But I've got this 'dream machine from 1993' that I occasionally bring out, and a functional serial modem would be a lovely thing.

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