I'm completely stumped by a problem with my raspberrypi board and hoping someone can help. I have a board connected to the gpio header, the board has a pic which sends a message which the pi receives. I've checked this with a screen session connected to ttyAMA0. I've tried to transmit characters back to the pic but they aren't received. I investigated a bit further and it looks like the pi isn't sending the characters in the first place. I connected a scope to the TXD pin on the GPIO and then use a python script to send messages as follows
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serialPort = serial.Serial("/dev/ttyAMA0", 9600, timeout=0.5, rtscts=False, dsrdtr=False, xonxoff=False,bytesize=serial.EIGHTBITS,parity=serial.PARITY_NONE)
Theres no signal coming from the tXD pin at all. When I send data to the pi frmo the pic, it receives it fine so I don't think I have the pins the wrong way round. That also shows that I have the right pin as I have gnd, TXD and RXD in a row (Also no signal on any pin).
Is there any chance i've blown up the uart? I have the data passing through an isolator with the pi side run off the 3.3v pin of the GIPO so very unlikely.