Could someone that has an RP-6 and CM-232 handy do me a favour?

Stick a multimeter between pin5(GND) and pin2(RX)... what DC voltage do you get?
Now try pin5(GND) and pin3(TX)?

Assuming the ground lead on the meter is on the pin5(GND), I get 0volts off the RX which is what you'd expect and +9volts from the TX. This is backwards from the serial ports on my laptop and several PCs that I've compared. They give -9volts across the same pins and this seems to match the RS-232 standard.

This difference seems to be messing up the control of a receiver that I'm trying to interface with via the CM-232. Laptop = Good but CM-232 = Bad... the only difference I can find is the reveresed voltage coming from the CM-232.

Thoughts?

Use a null modem adapter

Won't this just swap the RX and TX pins?

I think I've got the pins mapped correctly but the idle voltage on the TX pin seems to be inverted from what I see on the standard PC serial port.

This is the only difference that I can see during my investigation. All I know for sure is that the PC control works but I have issues when replacing the PC with the RP-6/CM-232 combo.

I think you're going to want to connect a cable between RS232 devices and then measure those voltages. This is just a suspicion, and I know it will be hard to get to those pins with a connector in place, but it could be that the open circuit voltage is unrelated to the voltage when you connect to another device. Pullups or pulldowns in the other device could make everything identical.

Or perhaps make the same measurements again, but with a 1000 ohm resistor in parallel with the voltmeter. That will act enough like a pullup or pulldown to tell you if a passive load in the other device changes the voltage. If it does, then you really need to measure the voltage with devices connected together.

What does RTI say about this? I know, it was 10:15 p.m. my time when you asked, but they're open now.

Chatted with them and they repeated the test on their end. The result is that a new CM-232 is being sent to me under the assumption that the module I have is defective. I'll update this post when it arrives. I'm hoping the update will be good news. :)

maybe somthing is wrong with the CM232, but I agree with ernie, I think the RP-6 (unlike a laptop) constantly provides power to the cm232 unless it is connected to some other device, so the only way to test this is under load.

connect the cm232 to your laptop via a null modem, use a hex reader utility http://www.rs232pro.com/ on the laptop, issue a command and see what the reader says

[Link: lammertbies.nl]

BTW, I have already met bad CM232 with very strange behavior, it sent data, but totally different than it should be, after exchanged, everything OK...