We recently bought a Plugable RS232 to USB adapter for communicating with a RS232 instrument (PID controller). The problem we are having is that the adapter works fine and communicated well when we are using a desktop computer - but stops working when we switched over to a laptop (able to send commands, but not able to read). Drivers and settings on the two computers are exactly the same.
Now, I don’t think this is completely the problem with the Plugable adapter, because the instrument manufacturer admitted that the output (RxD) from their instrument is not the standard +/-12V. Rather, we observed that on the TxD pin, the voltage is between -5 and 0V, and on the RxD pin the voltage is between 0 and +5V. I believe 0V is not defined in the RS232 standard, so I am wondering how is this handled by the Plugable adapter?
I have two questions:
- Why would the adapter work on the desktop but not on the laptop?
- If you think the non-standard voltage might be a problem, do you see any easy way to correct/circumvent this?
Thanks in advance for your help.