Pic18F4550 + SIMCOM SIM900D GSM/GPRS

[tacbanon]

Hello to everyone,
I have a SIMCOM SIM900D GSM/GPRS module. I'm trying to make it communicate with the Pic18F4550 with 20Mhz crystal. But before that I made sure that the module is working/replying to AT commands by connecting it the serial port communicator via USB - TTL converter. And I confirmed that PC(Serial communicator) -> USB-TTL converter + GSM(Baud 115200) module are working.


Then the next step I did is to try to send HSEROUT ["AT",13] to the GSM module..using hardware setup below

and this is the code I'm using...

 asm
    __CONFIG    _CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L
    __CONFIG    _CONFIG1H, _FOSC_HSPLL_HS_1H & _FCMEN_OFF_1H & _IESO_OFF_1H
    __CONFIG    _CONFIG2L, _PWRT_ON_2L & _BOR_ON_2L  & _BORV_2_2L  & _VREGEN_ON_2L   
    __CONFIG    _CONFIG2H, _WDT_OFF_2H 
    __CONFIG    _CONFIG3H, _MCLRE_ON_3H & _LPT1OSC_OFF_3H & _PBADEN_OFF_3H & _CCP2MX_ON_3H 
    __CONFIG    _CONFIG4L, _STVREN_ON_4L & _LVP_OFF_4L & _ICPRT_OFF_4L  & _XINST_OFF_4L & _DEBUG_OFF_4L 
endasm

        
        DEFINE OSC 48
        DEFINE HSER_RCSTA 90h ' enable serial port, 
        DEFINE HSER_TXSTA 36  ' enable transmit, * we change 20h to 36 for 115200          
        DEFINE HSER_BAUD 115200
        DEFINE HSER_CLOERR  1 ' automatic clear overrun error  
        
        TRISC  = %10000000    ' PORTC.7 is the RX input, PORTC.6 is the TX output
                              
    
    '   Serial communication definition
    '   ===============================
        '
ADCON1 = %00001111      'Set up ADCON1 register no matter what you're doing!!!!!!
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

INCLUDE "MODEDEFS.BAS"       ' Include Shiftin/out modes


'*****************************************************************************     




Serialdata var    byte

INTCON2.7 = 0        ' Enable PORTB pull-ups
TRISB = %11111000
TRISC = %10000000
led1 var PortC.0
TRISD = %00000000

 
Serout2 PORTD.5, 84, [$1B,$63,$30]  'cursor off for serial LCD
Serout2 PORTD.5, 84, [$1B,$45,"SMS DEBUG PORT"]   ' serial LCD
main:
PORTB = 0            ' PORTB lines low to read buttons

   If PORTB.4 = 0 Then ' If 1st button pressed...
     
      HSEROUT ["Button 1",13]
      Serout2 PORTD.5, 84, [$1B,$45, "SMS DEBUG PORT"]
      Serout2 PORTD.5, 84, [$D, "Button 1 "]
      pause 500
      Serout2 PORTD.5, 84, [$1B,$45,"SMS DEBUG PORT"]
      gosub GSM_CHECK 
   Endif
   pause 200   ' pause to avoid sending repetation

goto main

End   'End program


GSM_CHECK:
HSEROUT ["AT",13]                    'Send AT to modem followed by a CR
HSERIN 5000, GSM_CHECK_ERR, [WAIT("OK")] 'Check OK reply, wait 5sec max.
Serout2 PORTD.5, 84, [$D, "GSM OK"]
High PORTB.0     ' 1st LED on
PAUSE 1000
low PORTB.0
return

 GSM_CHECK_ERR:
 Serout2 PORTD.5, 84, [$D, "GSM ERROR"]   
 
 ;HSEROUT ["GSM_ERROR",13]
 Return

I tried to interchange C6 and C7 lines but still I'm not getting "OK" response...hope anyone can give a me hint what I'm missing in my setup.

Thanks in advance,
tacbanon