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. |
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. |
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. |
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 |
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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