interfacing 8051 with gsm modem

[hassan ali]

hi,sorry for my English
i want to interface gsm modem with 8051 using serial communication , but first i want to know if (GPRS/GSM-Modem
SINAUT MD720-3) must connect first to rs232 circuit or it has already inside it a rs232 circuit because on websites i read that not all modems needs to rs232 circuit and , please help me to know how to connect it to 8051 and send the at commands through 8051.

 

[FvM]

SINAUT MD720-3 is an industrial GSM/GPRS modem. It's exposing a 9-Pin Sub_D RS232 interface, so you'll need a TTL-to-RS232 level converter, e.g. MAX232 to connect the processor UART pins to the modem.

SINAUT MD720-3 is rather expensive compared to embedded GPRS modules, e.g. from SIMCOM, why you are using it?

 

[hassan ali]

first, thank u very much for ur answer
second i using it because , it's only the available modem in my faculty lab..

 

[hamidrezamaddah]

u can find it by measuring the voltage on pin 2 of DB9
if it is posetive, you dont need converter
if it is negative, you need converter