Im new here,dont know if this is the right section. I'm using the sim300 module to control a dc motor with text messages.I bought it on ebay. The problem is I cant find GND, Tx and Rx.In the PCB There ARE 3 pins, which are AUT,SD,ST and im sure those are GND,Tx and Rx but i cant tell which one it is.Can you guyz help me out about this??