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UART pin 20 Voltage swing

PostPosted: Thu May 19, 2011 9:18 am
by linkinpark32123
HI I have a problem using uart with my radio. I have verified that I am sending the correct signals and that the radio responds to those signal. I was doing some trouble shooting and it looks to me like when the dspic33 in the dev board does not drop close enough to 0 volts when it transitions. The line is high at 3.3V and drops to about 2V and does not pass the threshold voltage the the radio reads as a 0. I believe that the radio thinks the line is high the whole time. the attached img Image is the scope of when the micro controller sends out the command and Image is when i Have a Terminal send out the same signal and you can see the radio response.

Re: UART pin 20 Voltage swing

PostPosted: Thu May 19, 2011 9:47 am
by Andrew
Sounds like you have the dsPIC's I/O configured incorrectly ...

1) Verify that the radio's output swings properly over the full {VCC, 0V] range when _not_ connected to anything.

2) Using a current-limited (i.e., 5mA max) supply, verify that the dsPIC33 sees the input change over the full [VCC, 0V] range.

remember, as long as the input at the dsPIC is properly configured (hi-Z), then ** it has nothing to do with the voltage swing of what is feeding it **. If it is not hi-Z, then either it's still configured as an output and it's fighting the radio, or perhaps there's a pullup keepint it high, or the radio's output stages are damaged.