Gsm modem 8051

Hi everbody,i guess, i have some problem about 8051 control Gsm modem with AT command
i have Enfora Gsm modem(it have rs232 socket input) and 8051 board(it include AT89c51rc2 and max232)
1.i communicated 8051 to pc (19200,8bit no party,1 stop,handshake none )
2.i communicated gsm modem to pc (same values ,Firts i setup gsm modem(AT+IFC ,AT+ICF, AT&D0(dtr unable) command) ) i thinks ,hardware and synchronization is well (but just for PC)
but i could not communicate 8051 to Gsm modem, code is down (just send AT and response)

void SendAT(void)
{
        putchar('A');
        putchar('T');
        putchar(0x0d);

}


void main()
{

//******************************************

  IE=0x90;
  SCON=0x50;
  PCON=0x80;            // 2 much more baudrate (19200)
  TMOD=0x20;
  TL1=0xFD;
  TH1=0xFD;             // yaklasik 9600 bps(11.0592Mhz)
  TR1=1;                // Z/S 1'i çalistir.
  TI=1;                 // gönderilmeye hazir
  RI=0;

//***************************************************

      longwait(); //wait funk. nearly 2 sn

      SendAT();
      while(RI ==0) { //show display wait } //when i connect  8051 with gsm modem
                                            //program always wait here line but
                                            //connect 8051 to pc and pc send serial something
                                            //program continue working
                                            //i mean ,not coming response gms modem or
                                            //nothing  arrive gms modem

      if(RI==1 ){ //show display ok  }
      else{//show display error }

}

how can i do , thanks for all now(please write quick, i really need help)