Hi.

Start by copying the code you have in here with "<<code>> <</code>>" tags.

SIM900A is only working in specific countries. See here for details.

What speed are your terminal set to? start by using 19200 8N1, that should make a good connection.

What are you powering the SIM900A with? Is it just the module or is it a PCB with a voltage regulator?

Regards, Lerche

Hi Lerche

Yeah I am from India and SIM 900A works only here I am using baud rate at 9600 and tried at 19200 also but still no change After deep analysis i found that the frdm board is not generating any signal and it is not sending any command to the SIM 900A module. I declare D1,D0 as tx and rx and tried to read the signal on the arduino board but nothing happens This is my code

1. include "mbed.h"
2. include "SDFileSystem.h" Serial gsm(D1, D0); tx,rx Serial pc(USBTX, USBRX); DigitalOut dtr(D2); DigitalOut pwr_key(D3); int flag = 0; int8_t sendATcommand(char* ATcommand, char* expected_answer, unsigned int timeout){ uint8_t x=0, answer=0; char response[100]; time_t previous; memset(response, '\0', 100); wait_ms(100); while( gsm.readable() > 0) gsm.getc(); gsm.printf("%s \r", ATcommand); x = 0; previous = time(NULL); do{ if(gsm.readable() != 0){ response[x] = gsm.getc(); pc.putc(response[x]); x++; if (strstr(response, expected_answer) != NULL) { answer = 1; } }

}while((answer == 0) && ((time(NULL) - previous) < timeout)); return answer; } int8_t sendATcommand2(char* ATcommand, char* expected_answer1, char* expected_answer2, unsigned int timeout){ uint8_t x=0, answer=0; char response[100]; time_t previous; memset(response, '\0', 100); Initialize the string wait_ms(100); while( gsm.readable() != 0) gsm.getc(); Clean the input buffer

gsm.printf("%s \r", ATcommand); x = 0; previous = time(NULL); do{ if(gsm.readable() != 0){ response[x] = gsm.getc(); pc.putc(response[x]); x++; if (strstr(response, expected_answer1) != NULL) { answer = 1; } if (strstr(response, expected_answer2) != NULL) { answer = 2; break; } }

}while((answer == 0) && ((time(NULL) - previous) < timeout)); return answer; }

uint32_t do_list(const char *fsrc) { DIR *d = opendir(fsrc); struct dirent *p; uint32_t counter = 0;

while ((p = readdir(d)) != NULL) { counter++; printf("%s\n", p->d_name); } closedir(d); return counter; } void power_on_off() { pwr_key = 0; wait(2); pwr_key = 1; } void gsm_init() { int cnt = 0; gsm_wake(); pc.printf("\r\nI am 1"); gsm_wake(); while(sendATcommand("AT+CREG?", "+CREG: 0,1", 5) || sendATcommand("AT+CREG?", "+CREG: 0,5", 5) == 0) { pc.printf("\r\nI am 1.5"); sendATcommand("AT+CREG=1", "OK", 10); gsm.printf("OK"); wait(2); ++cnt; pc.printf("\r\nI am 2"); pc.printf("%d", cnt); if(cnt == 4) { pc.printf("GSM registration failed"); return; } } pc.printf("\r\nI am 3"); }

int main() { pc.printf("Hello World \r\n"); gsm.baud(9600); gsm_init(); sendATcommand("AT", "OK", 2); dtr = 0; }