I was hoping you guys could help me on connecting SIM900A GSM Modem with this TM4C123 micro controller. I connected the RS232 ports of TX, RX, GND and power ports to GND and +12V. should I connect the RS232(TTL Levels) too? (the yellow pin connectors). As you can see in the picture, the red LED turns on for about 64ms and off for 3s, which based on this website: https://elementztechblog.wordpress.com/2014/10/10/interfacing-sim900a-gsm-modem-with-arduino/ means its registered to network or SIM card is active. but Green LED should be on to indicate that it is working properly and ready to send and receive messages, right? Could someone please explain the pin connection for this modem. thanks in advance
The correct connections are: 3VR on GSM modem to TX port on launchpad, 3VT on GSM modem to RX port on launchpad and GND to GND. External Power supply too. you can test it with connecting the GSM modem to TTL to USB adapter and open putty and write "AT", if it replies "OK", its working.
For AT commands, you connect the modem with a UART interface with RX and TX of the board connected with TX and RX of modem. Connect GND of board to GND in modem. You have to send commands with UART interface and the modem would respond. You can type commands on terminal or send them with a command interface and check all responses with software. You can probably see responses of modem on a terminal.The voltage levels of RX and TX pins were probably 3.3V or 5V. SIMT,SIMR probably mean TX and RX of modem.