How to read serial output?

[JMC 353]

A device can be controlled using its computer program through serial port, rs232. How can I detect its commands exported through pin 2? I tried LabView serial examples, but it did not work. What I did is using one computer to run the device program, its output goes to serial pin 2 which is connected to pin 3 in another computer's serial port. And the second computer is set to LabView read condition.

Many thanks, JMC

[John Lum]

JMC,

It sounds as if you're doing the right things, but maybe you're confusing the transmit and receive lines. I think that the transmission would appear on output pin 3 in your case; it typically doesn't matter once you're connected to your device, because you typically use a null-modem cable that swaps 2 and 3 from one end to the other.

I'd highly encourage you to check out the Serial Support page on the NI Support site (http://www.ni.com/support/serlsupp.htm), paying particular attention to the "General Concepts" and "Getting Started" links. These pages provide a lot of good background for what you're trying to do.

In particular, I'd encourage trying a loop-back scenario using a single computer, making sure that works, then graduating to two machines and
a null-modem cable.

Hope it helps,
John Lum
National Instruments

[waldemar.hersacher]

Giving the pin number on a serial port can be confusing. There are two lines named Rx and Tx and they are on pin 2 and 3. The pins for Tx and Rx are swapped on 9 and 25 pin connectors.
There is another reason why the program wont receive anything. If the device uses hardware handshake with RTS/CTS you have to set the handshake lines to get any data.
Waldemar