Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
9 years, 9 months ago.
Attempting to use serial comms via I/O pins (not USB)
Taking the default examples, I've changed the PinName from USBTX,USBRX and switched them to physical I/O pins 9,11 on the nrf51822 mkit board.
However, after hooking them up to a PC, I get nothing over that communication channel. I have hooked up pin 9, 11, and GND to the cable leading to the PC (making sure that TX and RX wires are crossed).
Interestingly enough, I check the USB comm port, and communications are happening there.
What am I missing to have this serial I/O go over the physical I/O and not USB?
Question relating to:
1 Answer
9 years, 9 months ago.
According to the user manual USBTX is identical to P0_9 and USBRX is identical to P0_11. That explains why you still see comms through the USB serial interface. Note that the Pins carry 3V3 level signals and they should never be connected to a regular PC serial port (-12V..+12V). You must use a levelconverter (eg MAX3232) which will also invert the logic levels. Also note that it is not a good idea to short the TX pins from the PC side and from the onboard USB to serial converter. This will happen when both are connected at the same time. The handbook mentions that you can disable the onboard USB converter using SW4.