Receiving a lot of junk on serial

[qsa301]

I developed an interface in LabWin that I use to get information using the serial port. While it gives me some useful information, it also gives a lot junk characters on the terminal. I am running my serial connection at:  baudRate 115200, parity 0, dataBits 8, stopBits 1, inputQueueSize 5000, outputQueueSize 512. Any suggestions?

Thank you.

[zarnon]

Are you flushing the buffers?

I had a serial project that was giving me a lot of junk until I started calling FlushOutQ (iComPortNum) and FlushInQ(iComPortNum) before every send.

[qsa301]

Thank you Zarnon for your reply. but I was already using FlushInQ and FlushOutQ functions and I am still getting junk characters as well as missing some character while reading from the serial.

[menchar]

How do you know the junk isn't really there?

A bad cable could do this, or a very noisy environment, or a faulty device that's off on the bit clock by 5% or more.  Do you have a really long cable?  At that bit rate, you can't run it very far without getting into trouble.  rs-232 spec calls out cable length Vs. bit rate.

I used to hook up a dumb terminal like an HP 2392 to a suspect serial stream and eavesdrop on it - made it easy to spot bad stuff.

Do you have a frame ground connected between the PC and the other device?  A ground loop can cause problems.  Optically isolated port can solve this (NI sells these).

Are you using a USB / rs-232 converter by any chance?  Many of these are junk and just don't work reliably.

Does it run error free at a lower bit rate?

Menchar

[Ted_H]

Hi there,

What are you communicating with through your serial port?  Does your device have a programming manual?  A programming manual would tell you exactly what type of data to expect.  Could you elaborate on exactly what you are seeing, also on the data you are missing?

Thanks,

Ted

[qsa301]

Thank you mechar for your reply. You are right. I was using the USB to Serial connector, which apparently does not work that well and was giving me lot of junk. But I replaced that and everything was fine. The reason I was not sure whats happening was, when I use Tera Term or Hyper Terminal, I do not get all that junk but when i use the LabWin interface, I was getting all of that. I am still not sure. But I am not going to worry about it for now. Thank you for your help.