On Wed, 31 May 2006 17:32:00 GMT, Vey put finger
to keyboard and composed:

Vey wrote:
When a program asserts these to go high, the voltage is supposed to
increase to more than +3VDC, right?

Looking at my multimeter, mine aren't doing anything,

Well, I measured again. I see +0.03VDC and -0.03VDC on RTS Hi/Lo (pin4)
and -0.001VDC and -0.02VDC RTS Hi/Lo (pin7).

So maybe that explains the loopback test passing, but that's no where
near 3 volts and the literature says those readings are considered to be
"transitory" voltage.

IME these voltages toggle between approximately +10V and -10V. If the
COM port is idle, then the RTS and DTR outputs should be sitting at
one or the other of these levels. Just to be sure, are you using pin 5
as the signal ground?

I've written the following program to test COM ports:
http://www.users.on.net/~fzabkar/comstest.exe

It runs in DOS only. Each output pin is toggled at 1Hz, 0.5Hz, and
0.25Hz. A loopback function is also supported.

This old post of mine describes how to use the DOS Debug command to
directly control the DTR and RTS pins:
http://groups.google.com/group/comp....e=source&hl=en

- Franc Zabkar
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