I’m having some trouble with a GM862 cell module. I can’t get it to communicate like it should. Here’s what I do:
Step 1- To turn the module ‘on’, I pull the ‘ON_OFF’ pin (pin 17) low for 1 second (slightly more, technically). After this, the power supply shows an increase in the current draw (50mA before this, 200mA after). It’s a benchtop power supply with the current limit set at 3A, I’m using a LT1528 regulator, so I’m really doubting it’s a power supply issue (but I could be wrong).
Step 2- The datasheet recommends the baud rate between the GM862 and the host be set to 38400 (which it is). I send ‘AT’ for the ‘autobaud’ detection (per the GM862 datasheet), but the host IC (a SC16IS752 in this case) does not detect a response (though the oscilloscope shows that something serial-ish is coming back). If no response is detected after 200ms, ‘AT’ is sent again (and repeat until a response is received)
The catch- If I reset the microchip (a PIC16F88), it goes through steps 1 and 2 again. Step 1 ends up turning the GM862 OFF this time (not correct, but whatever)… but then, after step 2, there’s an ‘AT’ waiting in the serial receiver (note that the datasheet says the GM862 will return ‘OK’ after a good autobaud).
So I guess the question is: Why would the GM862 return a (valid) response as it’s being powered down and not while it’s powered up?
(Or why would the SC16IS752 only detect a valid response in the aforementioned scenario?)
Thanks in advance