Rhydo SIM 900 SIM 900 -TTL UART User manual

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Document : D a t a s h ee t Model # : G S M – 1936
Date : 10 - DEC -2011
SIM 900
SIM 900 SIM 900
SIM 900 -
--
-TTL
TTL TTL
TTL UART
UARTUART
UART
G
GG
GS
SS
SM/G
M/GM/G
M/GP
PP
PRS
RSRS
RS M
MM
Mo
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dd
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em
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User Manua l
Rhydo Technologies (P) Ltd.
(An ISO 9001:2008 Certified R&D Company)
Golden Plaza, Chitoor Road,
Cochin – 6 201 , Kerala State, India
Phone : [phone]
Cell : 0091- 99466 70444
Fa : 0091 - 4 4-2370579
E-mail : [e-mail], [e-mail]
WebSite : http://www.rhydolabz.com

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GSM/GPRS TTL -Modem from rhydoLABZ is built with SIMC OM Make SIM900 Quad-band
GSM/GPRS engine, works on frequencies 50 MHz, 900 MHz, 1 00 MHz and 1900 MHz. It is very
compact in size and easy to use as plug in GSM Modem. The Modem is designed with 3V3/5V TTL
interfacing circuitry, which allows you to directly interface to 5V microcontrollers( PIC,Arduino,AVR ect)
as well as 3V3 Microcontrollers ( ARM,ARM Cortex XX, ect) .The baud rate can be configurable from
9600-115200 through AT command. Initially Modem is in Autobaud mode. This GSM/GPRS TTL Modem is
having internal TCP/IP stack to enable you to connect with internet via GPRS. It is suitable for SMS as
well as DATA transfer application in M2M interface.
The modem needed only two wires (Tx,Rx) except Power supply to interface with
microcontroller/Host. The built in Low Dropout Linear voltage regulator allows you to connect wide range of
unregulated power supply (4.2V -13V). Yes, 5 V is in between !! .Using this modem, you will be able to send
& Read SMS, connect to internet via GPRS through simple AT commands.
FEATURES
 High Quality Product (Not hobby grade)
 Quad-Band GSM/GPRS
50/ 900/ 1 00/ 1900 MHz
 3V3 or 5V interface for direct
communication with MCU kit
 Configurable baud rate
 SMA connector with GSM L Type
Antenna.
 Built in SIM Card holder.
 Built in Network Status LED
 Inbuilt Powerful TCP/IP protocol stack
for internet data transfer over GPRS.
 Audio interface Connector
 Most Status & Controlling Pins are
available at Connector
 Normal operation temperature: -20 °C to
+55 °C
 Input Voltage: 5V-12V DC
SPECIFICATIONS
 Quad-Band 50/ 900/ 1 00/ 1900 MHz
 GPRS multi-slot class 10/
 GPRS mobile station class B
 Compliant to GSM phase 2/2+
o Class 4 (2 W @ 50/ 900 MHz)
o Class 1 (1 W @ 1 00/1900MHz)
 Dimensions: 24*24*3mm
 Weight: 3.4g
 Control via AT commands (GSM 07.07
,07.05 and SIMCOM enhanced AT Commands)
 Low power consumption: 1.0mA(sleep
mode)
 Operation temperature: -40°C to + 5 °C\
Specifications for Fa
 Group 3, class 1
Specifications for Data
 GPRS class 10: max. 5.6 kbps (downlink)
 PBCCH support
 Coding schemes CS 1, 2, 3, 4
 CSD up to 14.4 kbps
 USSD
 Non transparent mode
 PPP-stack
Specifications for SMS via GSM/GPRS
 Point to point MO and MT
 SMS cell broadcast
 Text and PDU mode
Software features
 0710 MUX protocol
 embedded TCP/UDP protocol
 FTP/HTTP
Special firmware
 FOTA
 MMS

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 Java (cooperate with Iasolution)
 Embedded AT
Specifications for Voice
 Tricodec
o Half rate (HR)
o Full rate (FR)
o Enhanced Full rate (EFR)
 Hands-free operation
 (Echo suppression)
 AMR
o Half rate (HR)
o Full rate (FR)
Interfaces
 Analog audio interface
 Serial interface
 SMA Antenna Connector
 Seriel Port Pins (RXD,TXD) at 2mm Pitch
RMC
 Seriel Port Status and Controlling Pins at
2mm Pitch RMC
 DC Power pins at 2mm Pitch RMC
Compatibility
 AT cellular command interface

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DIMENSIONS
OPERATING CONDITIONS
P
a
r
a
m
e
t
e
r
IN/OUT
Mi
n
i
m
u
m
M
a
x
i
m
u
m
U
n
i
t
Supply Voltage -
VIN
Input 4.2 13 V
Current
Consumption
--- 40 590 mA
V_Inter ace Input 2.5 6 V

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PIN DESCRIPTIONS
PIN
PIN NAME
DIR
DETAILS
VIN Power Supply PWR Power Supply Input (4.2-13V DC,1A)
GND Ground PWR Ground Level o Power Supply
V_
Inter ace
Inter acing
Voltage PWR
Inter acing Voltage Input or on board voltage level conversion (3V3 or 5V).
I the modem has to be inter aced with a 5V microcontroller, the input to this pin
should be 5V DC and i the modem has to be inter aced with a 3V3 microcontroller,
the input to this pin should be 3.3V DC.
TXD Transmit OUT Outputs data bytes at voltage Level same as the V_Inter ace Pin
– Usually connected to the Rx pin o the microcontroller
RXD Receive IN Receives data bytes at voltage Level same as the V_Inter ace Pin
– Usually connected to the TX pin o the microcontroller
GND Ground PWR Ground Level o Inter acing Signals
/RESET Reset Input IN
Active low Reset pin to reset the modem , Pull down this pin to reset the modem using a
open collector output or switch- Normally leave open
-No on board level Conversion
RTS Request to
send IN Used For hardware low control. I needed ,can be shorted with CTS using J1 at bottom
side, in de ault le t open—With on board level Conversion
CTS Clear to send OUT Used For hardware low control. I needed , can be shorted with RTS using J1 at
bottom side, in de ault le t open-—With on board level Conversion
PWRKEY Power Key IN Pin or MODEM On/O externally using open collector transistor or Switch.
-No on board level Conversion
NETLIGHT Net Led OUT Open Collector output or connecting the Connection status LED externally
-Use 1k ohm resistor in series with LED
STS Status LED OUT Open Collector output or connecting the Status LED externally
-Use 1k ohm resistor in series with LED
RI Ring indicator OUT Pin to interrupt the Host / Microcontroller to indicate Call, SMS, Error ect.
-No on board level Conversion
DTR Data Terminal
Ready IN Input pin used to switch the modem to and rom the command mode
- Normally leave open
-— With on board level Conversion

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OPERATING MODES
The table below briefly summarizes the various operating modes referred to in the following chapters.
Mode Function
Normal
operation
GSM/GPRS
S EEP
Modem
will automatically go into S EEP m
ode if DTR is set to high level
and there is no on air and no hardware interrupt (such as data on serial
port). In this case, the current consumption of GSM Modem will reduce to
the minimal evel.
In S EEP mode, the Modem can still receive paging message and SMS from
the system normally.
GSM IDLE
Software is active.
Modem
has registe
red to the GSM networ , and the
modem is ready to send and receive.
GSM TALK
Connection between two subscribers is in pr
ogress. In this case, the
power consumption depends on networ settings such as DTX off/on,
FR/EFR/HR, hopping sequences, antenna.
GPRS
STANDBY
Modem
is ready for GPRS data transfer, b
ut no data is currently sent or
received. In this case, power consumption depends on networ settings
and GPRS configuration.
GPRS DATA
There is GPRS data transfer (PPP or TCP or
UDP) in progress. In this
case,power consumption is related with networ settings (e.g. power
controllevel), uplin / downlin data rates and GPRS configuration (e.g.
used multi-slot settings).
POWER
DOWN
Normal shutdown by sending the “AT+CPOWD=1”
command or using the PWRKEY. The
power management ASIC disconnects the power supply from the baseband part of the
GSM Modem. Software is not active. The serial port is not accessible. Operating voltage
remains applied to the internal circuitry
Minimum
functionality
mode
(withoutremove
power
supply)
Use the “AT+CFUN” command can set the modem to a minimum functionality mode
without remove the power supply. In this case, the RF part of the modem will not wor
or the SIM card will not be accessible, or both RF part and SIM card will be closed, and
the serial port is still accessible. The power consumption in this case is very low.

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1.1 Turn on GSM Modem Using the PWRKEY Pin (Power on)
You can turn on the Modem by driving the PWRKEY to a low level voltage for a short time (2-3 sec) and then
release. This pin has pulled up to 2.9V in the GSM Modem. The simple circuit illustrates as the following figures.
1K PWRKEY
4.7K
BC547B
Turn on impulse
47K
Fig 6: Turn on GSM Modem using Open collector circuit
1.2 Turn Off GSM Modem
Following ways can be used to turn off the GSM Modem:
• Normal power down procedure: Turn off GSM Modem using the PWRKEY pin
• Normal power down procedure: Turn off GSM Modem using AT command
• Over-voltage or under-voltage automatic shutdown: Take effect if over-voltage or under-voltage is
detected
• Over-temperature or under-temperature automatic shutdown: Take effect if over-temperature or
under-temperature is detected
1.2.1 Turn Off GSM Modem Using the PWRKEY Pin (Power down)
You can turn off the GSM Modem by driving the PWRKEY to a low level voltage for a short time (2-3 sec) and then
release. Please refer to the turn on circuit above.
The power down scenario illustrates as following fig: 8.This procedure lets the modem log off from the network
and allows the software to enter into a secure state and save data before completely disconnecting the power
supply.Before the completion of the switching off procedure the GSM Modem will send out result code:
“NORMA POWER DOWN”

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After this moment, the AT commands can’t be executed. The modem enters the POWER DOWN mode. POWER
DOWN can also be indicated by STATUS pin, which is a low level voltage in this mode.
1.3 Turn Off GSM Modem Using AT Command
You can use the AT command “AT+CPOWD=1” to turn off the modem. This command lets the GSM Modem log off
from the network and allows the GSM Modem to enter into a secure state and save data before completely
disconnecting the power supply. Before the completion of the switching off procedure the GSM Modem will send
out result code:
“ NORMAL POWER DOWN”
After this moment, the AT commands can’t be executed. The GSM Modem enters the POWER DOWN mode, only
the RTC is still active. POWER DOWN can also be indicated by STATUS pin, which is a low level voltage in this
mode.
1.4 Restart GSM Modem Using the PWRKEY Pin
You can restart GSM MODEM by driving the PWRKEY to a low level voltage for a short time(2-3 sec) and then
release, the same as turning on GSM MODEM using the PWRKEY pin. Before restarting the GSM MODEM, you
need delay at least 500ms from detecting the STATUS low level on. The restarting scenario illustrates as the
following figure.
1.5 Power Saving
There are two methods for the GSM Modem to enter into low current consumption status. “AT+CFUN” is used to
set GSM Modem into minimum functionality mode and DTR hardware interface signal can be used to lead system
to be in S EEP mode (or slow clocking mode).
1.6 Minimum Functionality Mode
Minimum functionality mode reduces the functionality of the GSM Modem to a minimum and, thus, minimizes the
current consumption to the lowest level. This mode is set with the “AT+CFUN” command which provides the
choice of the functionality levels <fun>=0，1，4
• 0: minimum functionality;
• 1: full functionality (default);
• 4: disable phone both transmit and receive RF circuits;
If GSM MODEM has been set to minimum functionality by “AT+CFUN=0”, the RF function and SIM card function
will be closed. In this case, the serial port is still accessible, but all AT commands correlative with RF function or
SIM card function will not be accessible.
If GSM MODEM has been set by “AT+CFUN=4”, the RF function will be closed, the serial port is still active. In this
case all AT commands correlative with RF function will not be accessible.

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After GSM MODEM has been set by “AT+CFUN=0” or “AT+CFUN=4”, it can return to full functionality by
“AT+CFUN=1”.
For detailed information about “AT+CFUN”, please refer to document [1].
1.7 Sleep Mode (Slow Cloc Mode)
We can control SIM900 GSM Modem to enter or exit the S EEP mode in customer applications through DTR signal.
When DTR is in high level and there is no on air and hardware interrupt (such as GPIO interrupt or data on serial
port), GSM MODEM will enter S EEP mode automatically. In this mode, GSM MODEM can still receive paging or
SMS from network but the serial port is not accessible.
Note: For GSM MODEM, it requests to set AT command “AT+CSC K=1” to enable the sleep mode; the default
value is 0, that can’t make the GSM Modem enter sleep mode. For more details please refer to our AT command
list.
1.8 Wa e Up GSM MODEM from SLEEP Mode
When GSM MODEM is in S EEP mode, the following methods can wake up the GSM Modem.
• Enable DTR pin to wake up GSM MODEM.
If DTR pin is pulled down to a low level，this signal will wake up GSM MODEM from power saving mode.
The serial port will be active after DTR changed to low level for about 50ms.
• Receiving a voice or data call from network to wake up GSM MODEM.
• Receiving a SMS from network to wake up GSM MODEM.
1.9 Summary of State Transitions (except SLEEP mode)
The following figure shows how to proceed from one mode to another.
AT+CPOWD or Drive
PWRKEY to ground
Drive PWRKEY to ground
Normal Mode
PWR down
Mode

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2.0 Serial Interfaces
The GSM module is designed as a DCE (Data Communication Equipment), following the traditional DCE-DTE (Data
Terminal Equipment) connection. The GSM Modem and the client (DTE) are connected through the following
signal (as following figure shows). Autobauding supports baud rate from 1200bps to 57600bps.
Serial port
• TXD: Send data to the RXD signal line of the DTE
• RXD: Receive data from the TXD signal line of the DTE
serial port of the GSM engine supports autobauding for the following baud rates: 1200, 2400, 4800, 9600,
19200,38400 and 57600bps. Factory setting is autobauding enabled. This gives you the flexibility to put the
GSMengine into operation no matter what baud rate your host application is configured to. To take advantage
ofautobauding mode, specific attention should be paid to the following requirements:
Synchronization between DTE and DCE:
When DCE powers on with the autobauding enabled, user must first send “A” to synchronize the baud rate. It is
recommended to wait 2 to 3 seconds before sending “AT” character. After receiving the “OK” response, DTE and
DCE are correctly synchronized. The more information please refer to the AT command “AT+IPR”.
Restrictions on autobauding operation
• The serial port has to be operated at 8 data bits, no parity and 1 stop bit (factory setting).
• The Unsolicited Result Codes like "RDY", "+CFUN: 1" and "+CPIN: READY” are not indicated when you start
up the ME while autobauding is enabled. This is due to the fact that the new baud rate is not detected
unless DTE and DCE are correctly synchronized as described above.
Note: You can use AT+IPR=x to set a fixed baud rate and save the configuration to non-volatile flash memory.
After the configuration is saved as fixed baud rate, the Unsolicited Result Codes like "RDY" should be received
from the serial port all the time that the GSM MODEM is power on.
AT Command Syntax
When DCE powers on with the autobauding enabled, user must first send “A” to synchronize the baud rate. It is
recommended to wait 2 to 3 seconds before sending “AT” character. After receiving the “OK” response, DTE and
DCE are correctly synchronized The “AT” or “at” prefix must be set at the beginning of each Command. To
terminate a Command line enter <CR> , otherwise known as carriage return or \r.
Commands are followed by a response that includes <CR>< F><response><CR>< F>. Only the responses are
presented in the document here, <CR>< F> are omitted intentionally.

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Example: With ocal Echo enabled:
Transmit: AT\r
Receive: AT\r\r\nOK\r\n
SETTINGS FOR EASY MICROCONTROLLER COMMUNICATION
When communicating with the GSM Modem using a microcontroller, you usually want very short responses, no
local echo, and no startup messages.
Sticking on the &W to the end of the command saves the setting into memory.
ATV0&W\r Enable short response
ATE0&W\r Disable ocal Echo
AT+CIURC=0;&W\r Disable “CA READY” Startup Message
Now instead of commands returning OK or ERROR in plain text, as well as repeating all written commands, the
GSM Modem will not echo what you transmit and the GSM Modem will return error codes in single bytes. For
example, instead of:
Transmit: AT\r
Receive: \r\nOK\r\n
You’ll have:
Transmit: AT\r
Receive: \r\n0\r\n
SAMPLE AT COMMANDS CODE
1. PHONE COMMUNICATION
Goal: Call a phone
Dial 123-456-7890 = ATD1234567890;\r
This command returns OK or ERROR. Returns NO CARRIER when phone hangs up
2. SEND A TEXT MESSAGE
Goal: Send a text
AT+CMGF=1\r
Returns OK or ERROR

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AT+CSCS=”GSM”\r
Returns OK or ERROR
AT+CSCA=”[phone]” \r
Returns OK or ERROR. This number [phone] is the short
message center for AT&T/Cingular service. T-Mobile’s is [phone]
AT+CSMP=17,167,0,240\r
Returns OK or ERROR. These numbers refer to settings for text
message sending, keep them this way.
AT+CMGS=”
AT+CMGS=”1234567890”\r
Returns > , prompting what message to send. 1234567890 is the
phone number that the text message will be sent to.
Hello this is a message <Ctrl+z>
Type any message, then press <Ctrl+z>. Returns confirmation
message and Message ID number
3. SEND A TEXT MESSAGE
Goal: Read a Text
AT+CMGF=1\r
Returns OK or ERROR
AT+CMGDA=”DE A ”
Delete all text
AT+CNMI=0,0
Disable unsolicited error code
AT+CMGR=1
Read Message #1

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AT+CMG =”REC UNREAD”
Read all received unread messages
Debug port
• Null modem port
• Only contain Data lines TXD and RXD
• Debug Port used for debugging and upgrading firmware. It cannot be used for CSD call, FAX call. And the
Debug port can not use multiplexing function. It does not support autobauding function.
• Debug port supports the communication rates is 115200bps
2.1 Software Upgrade and Software Debug
The DBG_TXD, DBG_RXD and GND must be connected to the IO connector when user need to upgrade software
and debug software, the DBG_TXD, DBG_RXD should be used for software upgrade and for software debugging.
The TXD and RXD also should be connected to the IO connector, if user wants to send AT command or data stream
to GSM MODEM. The PWRKEY pin is recommended to connect to the IO connector. The user also can add a switch
between the PWRKEY and the GND. The PWRKEY should be connected to the GND when GSM MODEM is
upgrading software. Please refer to the following figure.
1K
Serial port I/O Connector
GSM MODEM
(DCE)
DBG_TXD
DBG_RXD
GND
PWRKEY
TXD
RXD
GND
PWRKEY

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2.2 Audio Interfacing
Pin Name Pin Num er Function
AIN/AOUT
MIC
1
Microphone
input
+
GND
2
Common ground
SPK
3
Audio
output+
The GSM Modem provides one analog input channel, AIN, which may be used for microphone. The electret
microphone is recommended when the interface is used for microphone. The outputs connect to the receiver.
Thereceiver outputs only can directly drive 32Ω.
External line inputs are available to directly mix or multiplex externally generated analog signals such as
polyphonic tones from an external melody IC or music generated by an FM tuner IC or module.
You can use AT+CMIC to adjust the input gain level of microphone, use AT+SIDET to set the side-tone level. In
addition, you can also use AT+C V to adjust the output gain level. For more details, please refer to document
It is suggested that you adopt one of the following two matching circuits in order to improve audio
performance.The difference audio signals have to be layout according to difference signal layout rules. As show in
following figures (Note: all components package are 0 03.) If you want to adopt an amplifier circuit for audio, we
recommend National Company’s M4890. Of course you can select it according to your requirement.

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INTERFACING THE GSM MODEM
 Interfacing t e Modem to microcontroller (Basic connection)
Fig:3 GSM Modem Interfacing with Microcontroller (Basic Connections)
The Modem can be directly interface with 5V microcontrollers like PIC ,AVR , 805 Derivatives , Arduinos and 3V3 Microcontrollers
like ARM ,ARM Cortex XX ect. Make ensure V_INTERFACE pin is supplied with same voltage level as the microcontroller VCC. As
per the Fig:3 there is only 2 connections are required to use the modem . Connect RX pin of the modem to the TX pin of the
microcontroller and TX pin of the modem to microcontroller’s RX pin. The connected power supply (4.2v to 2v dc) should be capable
of handling current up to A .

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 Interfacing t e Modem to ARDUINO
 Interfacing t e Modem to PC via MAX232 Voltage level converter

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GETTING STARTED
1) Insert SIM card
Open the SIM cardholder by sliding it as per the arrow mark and lift up. Insert the SIM card , so as to align
the chamfered corner suits in card holder .After inserting the SIM card, lock the holder by sliding it to the
opposite direction of arrow mark.
2) Connect The Antenna
Fix the Supplied RF antenna to the SMA Antennae connector and tighten it by Rotating the Nut (
Never rotate the antennae for tightening ).
3) Connect the Pins
Connect the GSM modem as per the circuit diagram provided
4) Power the Modem
Power the modem from suitable power supply, which is having enough current capacity (>1A).
5) Check the Status of the LEDs
PWR LED - Red LED will lit immediately
STS LED - Green LED will lit after 1-2 seconds
NET LED -Blue LED will starts to blink in fast for few seconds(Searching For Network) and
becomes slow blinking once the Modem registers with the Network.
6) Network LED
The Network LED indicates the various status of GSM module eg. Power on, Network registration &
GPRS c
onn ecti v it y. When the modem is powered up, the status LED will blink every second. After the
Modem registers in the network (takes between 10-60 seconds), LED will blink in step of 3 seconds. At
this stage you can start using Modem for your application.
7) Baud rate
The Baud rate supported by the modem is between 9600 and 115200. Make sure the host system is set
to the supported baud rate.
 T e modem automatically sets to t e baud rate of t e first command sent by t e ost system after
it is powered up.
User must first send “A” to synchronize the baud rate. It is recommended to wait 2 to 3
seconds before sending “AT” character. After receiving the “OK” response, Your Device and GSM Modem
are correctly synchronized.
So t ere is no need for setting t e baud rate using commands.
 Before You Start using t e modem, please make sure t at t e SIM card you inserted support t e
needed fe
atur e s and t ere is enoug balance in SIM.!!!

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Testing with a PC
1. Connect the GSM Modem to a PC Com port using a MAX-232 level conversion circuit or TTL- RS-
232/TTL-USB convertor and Power it Up.
2. Create a HyperTerminal (Windows tool for serial port communications) window with B a udr ate
9600 and connect it to the ComPort to which GSM is connected.
3. Type any AT command in the HyperTerminal window and you could see the modem
responding by sending “OK”.
Te r m i n a l Window on PC where G S M M o d e m i s c o nn e c t e d

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S
SS
SA
AA
AM
MM
MP
PP
PL
LL
LE
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/* This program module sends an SMS from the modem to a prefixed number */
void ma
i n()
{
SerialPortInit();
/* Serial Communication – 9600-N-8- */
Send2Gsm("AT\r\n"); /* Transmit AT to the module – GSM Modem sends
OK */ DelayS(2); /* 2 sec delay */
Send2Gsm("ATE0\r\n"); /* Echo Off */
DelayS(2); /* 2 sec delay */
Send2Gsm("AT+CMGF= \r\n"); /* Switch to text mode */
DelayS(2); /* 2 sec delay */
Send2Gsm("AT+CMGS=\"[phone]\"\r\n"); /* Send SMS to a cell number */
DelayS(2); /* 2 sec delay */
Send2Gsm("TEST DATA FROM RhydoLABZ-COCHIN"); /* Input SMS Data */
SerialTx(0x a); /* Ctrl-Z indicates end of SMS */
DelayS(2); /* 2 sec delay */
wh
il e( );
}
Function Description
SerialPortInit – Module to initialize serial communication parameters
Send2Gsm -- Module to transmit a string of data through Serial Port
S e r ial Tx – Module to transmit a byte through serial port

www.rhydolabz.com SIM900 GSM/GPRS TTL UART Modem - User Man al
W e b r i n g t h e w o r l d t o y o u … … . .
Page 20
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 Download setup file from www.rhydolabz.com/documents/gps_gsm/gsm_modem.zip
 Install the setup file in your PC. Once the installation is completed, open the application from
StartMenu-Programs-Rhydolabz-GSM Modem.
 Connect the GSM Modem to a PC Com port using a MAX-232 circuit or TTL-RS-232/TTL-
USB and Power it Up.
 Select the Comport* (in the application software) to which GSM modem is connected and Press
the “Connect” button.
 Click on the button “Test Modem Communication”. If the connection is OK, the software
displays “GSM Modem OK”.
 If you want to send an SMS to another mobile using the modem, type the SMS data and Mobile
Number (Add Country code as prefix) and click “Send SMS” button.
* If t e comport number to w ic t e modem is connected does not appear in t e software, re-assign t e
Comport to an available one.(Can be done in Device Manager- Comport-Properties)