Some months ago I bought a GM862-GPS module that have been working fine with a RS-232 connection to my PC. For that I use a MAX3232 at 3V.
Right now I’m trying to connect the GM862 module to my PIC18F4431 using the same method. I want to use a MAX3232 at the GM862 side and a MAX232 at the PIC18F4431 side for the USART level conversion. I know there are other methods to do the level conversion but right now I prefer this method for development purposes.
When I connect the GM862 to the computer everything works fine. When I connect PIC18F4431 to the computer everything works fine. My problem is when I connect GM862 to the PIC18F4431… the communication doesn’t seem to happen. I’ve checked and tested the code and I know it is ok. Do I need another cable configuration?
If both the GSM and PIC communicate with the PC, but don’t communicate with each other, you probably have the TX pins of both devices connected together and the RX pins of both devies connected together.
Now… how is this possible: my GM862 can read the AT commands from the PIC but the PIC can’t get the reply from the GM862. I can see by the status led that GM862 did the network registration correctly but the PIC doesn’t get the OK reply. I have tested the PIC code connecting it directly to the computer so I know it is correct.