I am able to make a serial connection with a serial debugger. The SARA-R4 bd acknowledges at most one character at a time and then ignores the remaining. It is not possible to send AT commands because of this. I followed Sparks hookup doc. and am using hardware serial, 3.3V and 115200 baud rate. I manually power up with the on board button. The board is flakely about powering on. It doesn’t do that reliably. I have two units, and both have problems.
The fact that both are being finnicky probably points to some other issue; have you tried an alternate PC/cable/port?
I read the SARA-R4 Ublox system integration document and they say that for this model -02B, the RTS must be held low for UART comms. Did that, and it is now working. I do not see anything in your hook up doc. about RTS.
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