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Topic: A6 GSM module Tx baud rate very high (Read 1 time) previous topic - next topic


I have the A6 gsm mini module and I think I've done all the obvious things
 - working SIM
 - its own 5v 2A power supply

I connected to an Arduino Uno and ran various programs, including a debug code that tries to find the right baud rate.  Nothing sensible was received from the module.

I tried the SSCOM32 test program, which produced the same results.

Basically the module sends data when it is initialised, but the data is interpreted as junk at whatever baud rate I try.

So I tried an oscilloscope.
I can see correct baud rates being used to send to the module.

However, the signal I see coming back (mainly at initialisation because it doesn't respond to anything I send) - the pulse width suggests a baud rate of about ten times the 'standard rate' of 115200 baud.  ie I am seeing what looks like serial transmission but with pulses of around one microsecond.

I have tried sending multiple 'AT' at 115200 baud and other speeds in case it is in autobaud mode and can sense my speed, but no response. 

I am baffled (or possibly missing something obvious of course!).  Can anyone shed light on this.

Peter A


Update:  I WAS missing something obvious!  Sorry to anyone else I baffled.

I was using the 'other' Tx/Rx pins on the A6 module.  Now that I am using the U_TX/U_RX pins, which are for the UART, it is working.
I don't know what the other pins are for, I haven't seen any mention of them.
I can see that the 'wrong' Tx pin seems to be sending at about 10x the standard 115200 baud.

I also found what has been mentioned elsewhere - that the software serial is unreliable at 115200 baud on a Uno.  I have been able to switch to a lower speed and then it is reliable.  I plan to use a Mega anyway.

I am also having some difficulty getting the A6 to initialise reliably, but have not yet had time to try the various tricks available.

Peter A

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