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By Sarek
I recently purchased a SparkFun branded BusPirate v3 board and am starting to learn my way around it. I was able to read an EEPROM for example. However I am trying to figure out something that should be much simpler, namely UART.

As I understand it, Live Monitor should show me what is being sent across the monitored wire connected to MOSI. With
Transparent bridge with both Tx and Rx connected I should be able to send in both directions?

The scenario is that I have the BP connected to the Arduino, MISO->Rx(UART Tx) and MOSI->Tx(UART Rx). The processor is held in RESET to prevent it sending/receiving anything and I am attempting to interact only with the UART. I have a terminal open to the Arduino and a second one to the BP, all at the same baud rate. I am seeing comms only in one direction, from the BP to the terminal, but not the other way around.

If I re-enable the processor and connect MISO to Rx then I can see the responses from the running sketch in Live monitor as expected.

If my understanding is correct, then why do I not get bi-directional communications in Transparent bridge?
By Sarek
Ok, it looks like I might have been given some inaccurate information. It seems that even if the processor is suspended by connecting RESET to GND, it will hold the Tx pin (pin 1) in a state that prevents a signal from being transmitted. So it is possible to connect with the UART Tx output via the Rx pin (pin 0) but not with the UART Rx, hence only one way communication is possible.

It would seem that it is not really possible to use the Arduino board as a UART to test something like a bluetooth module in command mode. A more appropriate approach would be to use something like an FTDI USB to serial converter board. They also have the advantage of supporting both 5v and 3.3v signalling.