I’m able to set up a data connection and transmit data but the characters I am sending to the GM862 are not received. Why?
The default flow control is hardware (RTS/CTS). Therefore your
application should be able to manage those lines. If your application
doesn’t use HFC then you have to disable it with AT&K0.
The hardware flow control works in this way:
the AVR has filled its receiving buffer and needs to stop the incoming
data from the module it RAISES to 3.V the RTS signal and the module will
stop sending data until the RTS is HIGH on the 2.8V interface ( note
that RS232 levels are inverted).
On the opposite direction, when
the module needs the AVR to stop sending data, it RAISES its CTS and the
AVR must stop sending data to the module until the CTS is HIGH.
For the other signals, you can ground the DTR and leave open the other control signals (RI, DSR).
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