Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Vey
 
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Default Serial DTR/RTS confusion

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, yet when I connect
DTR to DSR or RTS to CTS, they pass the loopback test.

Yes, my multimeter is set and working correctly. Yes, I am sure I am
looking it the right pins. I have tried every pin, just to make sure
(it's a 9 pin connection) and I don't see any voltage, plus or minus out
of any of the pins. Yet the loopbacks are working just fine.

I'm using Win2k and the B&B Electronics Comtest program.
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Vey
 
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Default Serial DTR/RTS confusion

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.
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Franc Zabkar
 
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Default Serial DTR/RTS confusion

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
--
Please remove one 'i' from my address when replying by email.
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Default Serial DTR/RTS confusion


Vey wrote:
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.


Are you measuring the output pins at the serial connector without a
load such as a modem on them. Remember a wrap block places the load of
a receiver onto the transmitter. Take a bare jumper and wire DTR to
DSR and look at the voltage level. You can do the same with RTS to
CTS. +3VDC is too low. I have seen good ones run anywhere from + or -
6volts to + or - 15 depending on the device.

Van Gardner

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Vey
 
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Default Serial DTR/RTS confusion

Franc Zabkar wrote:
just to be sure, are you using pin 5 as the signal ground?


Pin 5? As a ground? I had two different circuit diagrams I was working
from. Neither one mentioned connecting Pin 5 to the circuit's ground.
They both showed just the ground symbol.

Then when I was measuring, I was using the clam for a ground. Once I
used pin 5, everything measured right and then I connected Pin 5 to the
circuit and it started working and then just to check, I ohmed out the
clam to the ground on the PC and got nada.

Looking at a third similar circuit, it does mention ground going to pin 5.

Thanks Franc!


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