After you connect the wire(here PWRKEY(PIN 1) of SIM900 should be connected to GND during the whole process), first press START of Simcom - sim900 Customer flash loader V1.01 (before this process the module is power down, completely disconnect from any power) then power up the module( connect to power ). GPRS_TX and GPRS_RX should disconnect from other purpose. You can use the use the GPRS_TX and GPRS_RX pins with UartSBee or equal. I was not able to use the power key at all when GPRS_TX and GPRS_RX are connected. Press Start button in firmware update program.Press the power key, wait for the lights to be normal.Question: What is the exact procedure? I have tried various variations, but here’s what I am doing now: Question: Is it ok to use the GPRS_TX and GPRS_RX pins on the SIM900 board, or do I need to use the actual TXD and RXD pins on the SIM900 chip itself? (These pin numbers are looking into the male connectors on the computer end.)
I have connected pin 5 of the DB-9 RS-232 to ground, and pin 2 to the SIM900 board’s TX and pin 3 to the SIM900 board’s RX. I can’t quite get it to work, I get various different error messages and I’ve attached two. I think you can try to upgrade the firmware of SIM900, please down load the firmware and tool (including how) from : /images/8/ … d_tool.zip
