cctalk Digest, Vol 70, Issue 3

cctalk-request at classiccmp.org wrote: Huh? The RS-232-port isn't supposed to deliver any power at all. Some devices admittedly abused the RS-232 by using something like DTR to actually supply the power needed to drive the thing, but that is abuse. But I'd be surprised if a circa-70s modem was ever designed to use the power from the RS-232 port to drive the modem itself. I'd expect it to have an external power supply. The problem description is a bit vague. How do you know it is generating incorrect tones? Have you used a frequency analyser to check the tone frequencies? Or might it just be that what has been observed is that the modem don't work when used with the USB-to-serial? If so, then we have a number of possible problems, none of which neccesarily is a problem with the modem. Or is it just a case of listening to the modem while plugging in the cable, and not the same thing happening on the different serial ports. Might the USB-to-serial not start driving signals until something talks to it on the software side? I'd start by checking that the USB-to-serial really delivers correct voltages. Break out the oscilloscope. Next, I'd check if the USB-to-serial is happy without all kind of signal "right", and if the modem supplies all the "right" signals. Also check cables. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol