SIM900A GSM/GPRS Modem (RS-232)

SIM900A GSM/GPRS Modem (RS-232)
This modem is built with SIMCOM SIM900A a Dual-band
GSM/GPRS engine.
The Modem is designed with RS232 level converter
circuitry, which allow user to directly interface with serial
port of computer.
Default modem is in Auto baud rate mode, can be configure
it from 9600-115200 using AT commands.
 Supports Serial port(RS232), Audio interface, RTC,
Phonebook Management.
Internal TCP/IP stack to enable internet via GPRS.
Supports SMS as well as DATA transfer application in M2M
As far as design concerned, it is very compact design and
easy to use.
 Widely used in wireless communication projects.
Supply Voltage: 5-12V DC.
Temperature range : -30 DegC to +80 DegC.
LED indication for power and network status.
On board switching type power supply regulator with Buzzer to
indicate Call Alerts.
Transmitting power:
- Class4 (2W).
- Class1 (1W).
GPRS Connectivity:
- GPRS multi-slot class10 (default)
- GPRS multi-slot class8 (option)
Supports CSD, USSD, SMS, FAX (Group 3 Class 1).
Single SIM card and SMA connector with GSM Antenna.
 Serial port(RS232) output and supports for Audio interface,
RTC, Phonebook Management.
Connection Details
Connection Details
Sr. No. Connection / Terminal
1 DC Jack (X8)
DC Input
7-15 VDC Input
2 DB9 Female Conn (X4)
RS232 Connector
3 RJ11-4 Conn (X3)
Audio Connector
4 TX (X1-1)
Transmit Pin of SIM900
5 RX (X1-2)
Receive Pin of SIM900
6 ADC (X2-1)
ADC Input Pin
Input Voltage Range 0V to 2.8VDC
7 RTC (X2-2)
Power Supply for RTC
3V External Battery
8 DTX (X2-3)
9 RTX (X2-4)
10 GND (X2-5)
11 +5V (X2-6)
12 POUT (X3-1)
Debug Tx
Debug Rx
+5VDC Out Pin
for debugging and upgrading
Circuit Ground
+5DC 200mA Max
13 DTR (X3-2)
Data Terminal Ready
14 DCD (X3-3)
Data Carrier Detect
15 DBR (X3-4)
16 CTS (X3-5)
17 RTS (X3-6)
Clear to send
Request to Send
18 SCL (X4-1)
I2C Serial Bus Data
19 SDA (X4-2)
20 PWM1 (X4-3)
21 PWM2 (X4-4)
I2C Serial Bus Clk
On HyperTerminal connect modem with setting as below :
parity: None,
data bits: 8,
stop bits:1
All commands should be executed by pressing “Enter’ button.
To check Communication of modem:
command: AT
Reply: OK
Make Call:
command: ATD975648XXXX;
Reply: OK
Answer Call:
command: ATA
Reply: OK
Disconnect Call:
command: ATH
Reply: OK
Send SMS :
1) Set SMS configuration(Text mode only once):
command: AT+CMGF=1
Reply: OK
2) Send SMS :
command: AT+CMGS=“+91 975648XXXX”
>This is a test SMS<Ctrl+z>
Reply: +CMGS:45
Read SMS (location no: 1):
command: AT+CMGR=1
Reply: +CGMR: “REC UNREAD”,” 91 975648XXXX”
This is test SMS
Read SMS (location no: 2):
command: AT+CMGR=2
Reply: +CGMR: “REC UNREAD”,” 91 975648XXXX”
Hello how are you test SMS
Delete SMS at location 1:
command: AT+CMGD=1
Reply: OK
To Delete All SMS:
command: AT+CMGDA=“DEL ALL”
Reply: OK
To Read all SMS :
command: AT+CMGL=“ALL”
Reply: +CGML: 1,“REC READ”,” 91 975648XXXX”
This is test SMS
+CGMR: 2,“REC UNREAD”,” 91 975648XXXX”
Hello how are you test SMS
Note: For more details go to “” and search for
“SIMCOM SIM900A AT Command”. For SIM900A Datasheet
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