interfacing GSM module with PIC

[rookie]

i try interfacing GSM module connect with SK40c using PIC 16F877A by UART.
MAX 232 is connected between the PIC and GSM module.
the baud rate been set to 115200.
when i sending out 'at' from PIC,no reply back from GSM module as i am expected will receiving 'ok' as reply...
To verify whether the UART connection is ok, i change the baud rate to 9600 and connect it with RFID reader and it is function...

is it bacause of the other pin that are needed for serrial port like DTS, CTS, etc??
If it is, then how to solve it because PIC doesn't have the pin provided??
do i need to write software to solve it??
any clue??

[waiweng83]

Try to short the CTS and RTS pin from the GSM modem together.

Have you try to interface your GSM modem with the PC? Try it with hyper terminal, see whether u get any respond or not.

[rookie]

yes...it working well with PC...
why the reason to short CTS and RTS??
Thanks...

[ober]

CTS and RTS is for hardware hand shaking. Since PIC do not have that function, shorting both pin at GSM modem will disable the handshaking, thus sending data and receiving data anytime.

[waiweng83]

The CTS/RTS pin is for hardware flow control. It is used to inform the host that the device is ready to receive data and vice versa. If you do not want to implement the flow control in your MCU, you just loop it back to the GSM modem. It will assume your MCU is always ready for data.

[rookie]

get it...thankyou very much...

[ober]

rookie, do let us know your project progress.

It will be great if you share it here.

[rookie]

Basically my project title is 'attendance information system by using RFID and SMS service'
the function flow like children scan tag and SMS will sent to inform parents.
i use a SK40c,RFID reder and GSM module...
the source code basically combination of PR8 and PR27 because of PIC 16F877A only support 1 build in UART...and i am adding circuit the door lock of PR25 and trying to write to eeprom when a tag detected and sending data to hyper terminal by UART to USB converter when a SW was press...
now stuck with the circuit of door lock,because i replace the door lock by LED,suppose the LED will OFF when tag detected but it always ON and no idea how write and from eeprom although trying the code from user manual of hi-tech compiler...
any clue to continue it??thanks...

[waiweng83]

Do it part by part. Don't save the RFID code in your EEPROM 1st. Try to hard code it in your program. After success, then only try to store the RFID code in the EEPROM.

[vjn86]

hi waiweng83,

i would like to ask regarding the shorting dts and rts. I'm able to send sms through both hyperterminal and PIC16f7784a..However when receiving sms(that is to read it using at+cmgr=1), the microcontroller is not responding..Is is still due to cts and rts ?