Q: USB serial port give random data when.....

I have a single ATMEGA32 connected to a LT1082. An external 5V supply runs that board.

I am using a USB serial port adaptor to talk to my PC. The USB serial port gives random data when connected.

This happens with my laptop as well at my deskyop computers.

Any suggestions of why this is doing this ???

I checked the ground line from the LT1082 to the computer chassis.

I have tried a second LT1082.

Thanks for any ideas.


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Darn it. I had a VERY similar problem working with a very similar system (MAX232A and ATmega32). It was very baffling. I just can't remember what the details were at the moment, but it was nothing to do with the microcontroller per se.

I do remember that the "eureka!" moment came when I scoped the AVR side and the RS232 side of the MAX232 chip. I believe that I also had to change USB-serial modules - I think I was using a Cypress M8-based cheapo cable with the USB interface integrated into the DE9 molded backshell, and I had to upgrade to a Keyspan adapter. I suspected grounding problems too, but it wasn't as simple as that.

I also remember starting to post a really long description of where I was, what tests I had performed, etc. and begging for help. But I didn't click Post on it, because at the last moment I had the above brainwave.

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