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Serial communication problems

Posted: Tue Apr 03, 2007 4:27 am
by sst
I'm having trouble reading data from /dev/ttyS1 into my SAM9260-EK board
I have a 2.6.20 kernel compiled for the board (dmesg shows all 3 com ports intialized).
If I hook up another 3.3V micro (common grounds) via SCI to COM1 (i.e. ttyS1) I can't see any data if I run ttylog or programs like that for serial data.

from the digital standpoint I matched up speeds/stop bits/flowcontrol off etc.

From an electrical stand point the wierd thing that happens is if I have my 8bit micro's Tx line hooked up to a scope and a logic analyzer I can see the data fine, but as soon as I hook it up to the SAM9260 the scope shows the signals ground moved up by 500mV (but the signal looks okay, clean edges etc), but the logic analyser can no longer decode the data.

does any one have any code/setups that is known to work for serial communications?

Posted: Thu Apr 05, 2007 10:40 pm
by sst
okay so I found the problem, if any one is interested here's the solution:

the RS232 driver which is also connected to the pin I was trying to plug into was pulling up the line and wasn't letting it switch cleanly from the other micro.
so the simple soln. is to remove R106 which effectively does not enable the MAX324 hence tristating its pins.