Problem with RS-232 interfacing

dhruvil_90 · Joined: 09 Apr 2012 Posts: 1

Hey guys. I have a problem with interfacing my bluetooth module (aubtm-20) with Atmega 640. The BT module works perfectly and responds to the commands sent when connected directly to a PC. I have also debugged the code and it works perfectly. But when I connect the BT module (Rx and Tx pins are connected to MAX232 and then to DB9 connector) to the microcontroller using DB9 connector + MAX232, I get incomplete response.

For example, instead of getting getting the response as "<CR><LF>OK<CR><LF>", I get a response like "<CR><LF>O<LF><CR><LF>". The response I get seems to be a part of the actual response but I get a different response everytime.

Rx of BT module is connected to Tx of microcontroller and Tx of BT module is connected to Rx of microcontroller.

I also have shorted grounds of both the boards and have ensured that the baud rates are proper.

Please let me know what the problem could be.

hgrueneis · Joined: 04 Apr 2009 Posts: 906 Location: A-4786 Brunnenthal

Hard to tell without the code and any other info.
Did you check the status report to see the %-deviation of the com?
Sometimes setting the internal pull-up on RX helps.
Hubert

edit: What you post looks like a character overrun.
Mostly happens if you spend too much time in an ISR.
Do you use serial buffer or polling...bytematch....???