Technical Support
Staff member
Normally should be MCU_Tx - GSM_URx & MCU_Rx - GSM_UTx
That's normally the way it is, Tx (tramsit) from something goes into Rx (receive) or something else.

But if you are receiving the "OK" which only the module is sending then, however it is connected, would seem to be correct.

It could be down to how the module manufacturer has labelled their carrier PCB rather than than the way the SIM900 unit itself would have it.


Senior Member
Hi hippy,
I got SIM900 to work ($22 did it). I had to give up Goouuu Tech IOT-GA6 - same pgm gave different results.
Thank you