UART pin 20 Voltage swing

[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 is the scope of when the micro controller sends out the command and is when i Have a Terminal send out the same signal and you can see the radio response.

[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.