SimCom SIM900D EVB Supplement

a
SIM900D_Hardware
Design_V1.04

SIM900D Hardware Design
Document Title: SIM900D Hardware Design
Version: 1.04
Date: 2010-10-09
Status: Released
Document Control ID: SIM900D_Hardware Design_V1.04
General Notes
SIMCom offers this information as a service to its customers, to support application and engineering efforts
that use the products designed by SIMCom. The information provided is based upon requirements
specifically provided to SIMCom by the customers. SIMCom has not undertaken any independent search
for additional relevant information, including any information that may be in the customer’s possession.
Furthermore, system validation of this product designed by SIMCom within a larger electronic system
remains the responsibility of the customer or the customer’s system integrator. All specifications supplied
herein are subject to change.
Copyright
This document contains proprietary technical information which is the property of SIMCom Limited,
copying of this document and giving it to others and the using or communication of the contents thereof, are
forbidden without express authority. Offenders are liable to the payment of damages. All rights reserved in
the event of grant of a patent or the registration of a utility model or design. All specification supplied
herein are subject to change without notice at any time.
Copyright © Shanghai SIMCom Wireless Solutions Ltd. 2010
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Contents
Contents .....................................................................................................................................................................3
Version history...........................................................................................................................................................7
1 Introduction.............................................................................................................................................................8
1.1 Related Documents .......................................................................................................................................8
1.2 Terms and Abbreviations...............................................................................................................................8
1.3 Safety Precautions....................................................................................................................................... 11
2 SIM900D Overview..............................................................................................................................................13
2.1 SIM900D Key Features...............................................................................................................................13
2.2 SIM900D Functional Diagram....................................................................................................................15
2.3 SIM900D Evaluation Board........................................................................................................................16
3 Application Interface.............................................................................................................................................18
3.1 SIM900D Pin Description...........................................................................................................................18
3.2 Operating Modes.........................................................................................................................................21
3.3 Power Supply ..............................................................................................................................................22
3.3.1 Power Supply Pins.............................................................................................................................23
3.3.2 Minimizing Power Losses .................................................................................................................23
3.3.3 Monitoring Power Supply .................................................................................................................24
3.4 Power Up and Power Down Scenarios........................................................................................................24
3.4.1 Turn on SIM900D .............................................................................................................................24
3.4.2 Turn Off SIM900D............................................................................................................................26
3.4.3 Restart SIM900D Using the PWRKEY Pin ......................................................................................28
3.5 Charging interface .......................................................................................................................................28
3.5.1 Battery pack characteristics...............................................................................................................29
3.5.2 Recommended battery pack ..............................................................................................................29
3.5.3 Implemented charging technique.......................................................................................................30
3.5.4 Operating modes during charging .....................................................................................................31
3.5.5 Charger requirements ........................................................................................................................32
3.6 Summary of State Transitions (except SLEEP mode).................................................................................32
3.7 Power Saving ..............................................................................................................................................33
3.7.1 Minimum Functionality Mode ..........................................................................................................33
3.7.2 Sleep Mode I (CSCLK=1).................................................................................................................33
3.7.3 Wake Up SIM900D from SLEEP Mode (CSCLK=1) ......................................................................34
3.7.4 Sleep Mode II (CSCLK=2) ...............................................................................................................34
3.7.5 Wake Up SIM900D from SLEEP Mode (CSCLK=2) ......................................................................34
3.8 RTC Backup ................................................................................................................................................34
3.9 Serial Interfaces...........................................................................................................................................36
3.9.1 Function of serial port & debug port supporting ...............................................................................37
3.9.2 Software Upgrade and Software Debug ............................................................................................38
3.10 Audio Interfaces ........................................................................................................................................40
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SIM900D Hardware Design
3.10.1 Speaker Interface Configuration......................................................................................................41
3.10.2 Microphone Interfaces Configuration .............................................................................................42
3.10.3 Earphone Interface Configuration ...................................................................................................42
3.10.4 Referenced Electronic Characteristics.............................................................................................43
3.11 SIM Card Interface....................................................................................................................................44
3.11.1 SIM Card Application......................................................................................................................44
3.11.2 Design Considerations for SIM Card Holder ..................................................................................45
3.12 LCD Display Interface ..............................................................................................................................48
3.13 ADC ..........................................................................................................................................................48
3.14 Behaviors of the RI ...................................................................................................................................49
3.15 Network Status Indication.........................................................................................................................50
3.16 General Purpose Input Output (GPIO)......................................................................................................51
3.17 PWM .........................................................................................................................................................51
4 Antenna Interface ..................................................................................................................................................53
4.1 Module RF Output Power ...........................................................................................................................53
4.2 Module RF Receive Sensitivity...................................................................................................................53
4.3 Module Operating Frequencies ...................................................................................................................53
5 Electrical, Reliability and Radio Characteristics...................................................................................................54
5.1 Absolute Maximum Ratings........................................................................................................................54
5.2 Operating Temperatures..............................................................................................................................54
5.3 Power Supply Ratings .................................................................................................................................54
5.4 Current Consumption ..................................................................................................................................56
5.5 Electro-Static Discharge..............................................................................................................................56
6 Mechanics .............................................................................................................................................................58
6.1 Mechanical Dimensions of SIM900D.........................................................................................................58
6.2 Top and Bottom View of the SIM900D.......................................................................................................60
6.3 PIN Assignment of SIM900D.....................................................................................................................60
6.4 The Ramp-Soak-Spike Reflow Profile of SIM900D...................................................................................62
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SIM900D Hardware Design
Table Index
TABLE1: RELATED DOCUMENTS ................................................................................................................................8
TABLE2: TERMS AND ABBREVIATIONS .................................................................................................................... 8
TABLE3: SIM900D KEY FEATURES............................................................................................................................ 13
TABLE4: CODING SCHEMES AND MAXIMUM NET DATA RATES OVER AIR INTERFACE ............................. 15
TABLE5: PIN DESCRIPTION ........................................................................................................................................ 18
TABLE6: OVERVIEW OF OPERATING MODES......................................................................................................... 21
TABLE7: SPECIFICATION OF RECOMMENDED BATTERY PACK......................................................................... 30
TABLE8: CHARGE OPERATING MODES ................................................................................................................... 31
TABLE9: AT COMMAND USUALLY USED IN CHARGE-ONLY MODE ................................................................. 32
TABLE10: THE CURRENT CONSUMPTION OF DIFFERENT CONFIGURATION OF AT+CFUN......................... 33
TABLE11: PIN DEFINITION OF THE SERIAL INTERFACES ................................................................................... 36
TABLE12: LOGIC LEVELS OF THE SERIAL PORT AND DEBUG PORT ................................................................ 37
TABLE13: PIN DEFINITION OF THE AUDIO INTERFACES .................................................................................... 40
TABLE14: MIC INPUT CHARACTERISTICS .............................................................................................................. 43
TABLE15: AUDIO OUTPUT CHARACTERISTICS ..................................................................................................... 43
TABLE16: PIN DEFINITION OF THE SIM INTERFACE ............................................................................................ 44
TABLE17: PIN DESCRIPTION (AMPHENOL SIM CARD HOLDER) ....................................................................... 46
TABLE18: PIN DESCRIPTION (MOLEX SIM CARD HOLDER) ............................................................................... 47
TABLE19: PIN DEFINITION OF THE LCD INTERFACE ........................................................................................... 48
TABLE20: ADC SPECIFICATION ................................................................................................................................. 48
TABLE21: BEHAVIOURS OF THE RI........................................................................................................................... 49
TABLE22: WORKING STATE OF THE NETLIGHT .................................................................................................... 50
TABLE23: PIN DEFINITION OF THE GPIO INTERFACE.......................................................................................... 51
TABLE24: PIN DEFINITION OF THE PWM ................................................................................................................ 52
TABLE25: SIM900D CONDUCTED RF OUTPUT POWER......................................................................................... 53
TABLE26: SIM900D CONDUCTED RF RECEIVE SENSITIVITY ............................................................................. 53
TABLE27: SIM900D OPERATING FREQUENCIES..................................................................................................... 53
TABLE28: ABSOLUTE MAXIMUM RATINGS............................................................................................................ 54
TABLE29: SIM900D OPERATING TEMPERATURE ................................................................................................... 54
TABLE30: SIM900D POWER SUPPLY RATINGS........................................................................................................ 55
TABLE31: SIM900D CURRENT CONSUMPTION (VBAT=3.8V) .............................................................................. 56
TABLE32: THE ESD ENDURE STATUE MEASURED TABLE (TEMPERATURE: 25℃, HUMIDITY:45% ) ......... 57
TABLE33: PIN ASSIGNMENT....................................................................................................................................... 61
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Figure Index
FIGURE1: SIM900D FUNCTIONAL DIAGRAM ......................................................................................................... 16
FIGURE2: TOP VIEW OF SIM900D EVB ..................................................................................................................... 17
FIGURE3: REFERENCE CIRCUIT OF THE VBAT INPUT ......................................................................................... 22
FIGURE4: REFERENCE CIRCUIT OF THE SOURCE POWER SUPPLY INPUT...................................................... 23
FIGURE5: VBAT VOLTAGE DROP DURING TRANSMIT BURST ........................................................................... 23
FIGURE6: THE MINIMAL VBAT VOLTAGE AT VBAT DROP................................................................................... 24
FIGURE7: TURN ON SIM900D USING DRIVING CIRCUIT ..................................................................................... 25
FIGURE8: TURN ON SIM900D USING BUTTON ....................................................................................................... 25
FIGURE9: TIMING OF TURN ON SYSTEM USING PWRKEY ................................................................................. 25
FIGURE10: TIMING OF TURN OFF SYSTEM USING PWRKEY.............................................................................. 27
FIGURE11: TIMING OF RESTART SIM900D .............................................................................................................. 28
FIGURE12: SIM900D WITH BATTERY CHARGER AND PACK CONNECTION..................................................... 29
FIGURE13: CHARGE STATE TRANSITION................................................................................................................ 32
FIGURE14: RTC SUPPLY FROM NON-CHARGEABLE BATTERY .......................................................................... 35
FIGURE15: RTC SUPPLY FROM RECHARGEABLE BATTERY ............................................................................... 35
FIGURE16: RTC SUPPLY FROM CAPACITOR ........................................................................................................... 35
FIGURE17: SEIKO XH414H-IV01E CHARGE CHARACTERISTICS........................................................................ 36
FIGURE18: CONNECTION OF THE SERIAL INTERFACES ..................................................................................... 37
FIGURE19: CONNECTION OF SOFTWARE UPGRADE AND SOFTWARE DEBUG .............................................. 39
FIGURE20: RS232 LEVEL CONVERTER CIRCUIT.................................................................................................... 39
FIGURE21: SPEAKER INTERFACE CONFIGURATION ............................................................................................ 41
FIGURE22: SPEAKER INTERFACE WITH AMPLIFIER CONFIGURATION ........................................................... 41
FIGURE23: MICROPHONE INTERFACE CONFIGURATION.................................................................................... 42
FIGURE24: EARPHONE INTERFACE CONFIGURATION......................................................................................... 42
FIGURE25: REFERENCE CIRCUIT OF THE 8-PIN SIM CARD HOLDER ............................................................... 45
FIGURE26: REFERENCE CIRCUIT OF THE 6-PIN SIM CARD HOLDER ............................................................... 45
FIGURE27: AMPHENOL C707 10M006 512 2 SIM CARD HOLDER......................................................................... 46
FIGURE28: MOLEX 91228 SIM CARD HOLDER ....................................................................................................... 47
FIGURE29: RI BEHAVIOUR OF VOICE CALLING AS A RECEIVER ...................................................................... 49
FIGURE30: RI BEHAVIOUR OF DATA CALLING AS A RECEIVER ........................................................................ 49
FIGURE31: RI BEHAVIOUR OF URC OR RECEIVE SMS ......................................................................................... 50
FIGURE32: RI BEHAVIOUR AS A CALLER................................................................................................................ 50
FIGURE33: REFERENCE CIRCUIT OF NETLIGHT ................................................................................................... 51
FIGURE34: SIM900D TOP MECHANICAL DIMENSIONS......................................................................................... 58
FIGURE35: SIM900D BOTTOM MECHANICAL DIMENSIONS ............................................................................... 58
FIGURE36: SIM900D SIDE MECHANICAL DIMENSIONS ....................................................................................... 59
FIGURE37: RECOMMENDED PCB DECAL (UNIT: MM).......................................................................................... 59
FIGURE38: TOP AND BOTTOM VIEW OF THE SIM900D ........................................................................................ 60
FIGURE39: SIM900D PIN OUT DIAGRAM (TOP VIEW) ........................................................................................... 60
FIGURE40: THE RAMP-SOAK-SPIKE REFLOW PROFILE OF SIM900D................................................................ 62
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SIM900D Hardware Design
Version history
Date Version Description of change Author
2010-03-31 1.01 Origin Jing.zhou
Changed GHOST mode to Charge-only mode
§3.4.1.1Update the Figure8: Timing of turn on system
using PWRKEY
§3.4.2.1Update the Figure9: Timing of turn off system
using PWRKEY
2010-04-09 1.02
§4.2Update the Table25: SIM900D conducted RF
receive sensitivity
Jing.zhou
§3.8, Modify the VRTC pin connection when backup is
not needed.
§2.1, §3.3. §3.4 Modify the power supply range from
3.4V~4.5V to 3.1V~4.8V.
2010-06-24 1.03
§3.4.1.1Update the Figure8: Timing of turn on system
using PWRKEY
Jing.zhou
2010-10-09 1.04 Modify the power supply range to 3.2V~4.8V.
§3.3.2 Add Figure6: The minimal VBAT voltage at
VBAT drop
§3.4 Modified figure7，figure8，figure11.
§3.6 Add 3.6.4 and 3.6.5 description.
§3.11.1 Update the Figure25
§3.7 Update the Figure13
Jing.zhou
SIM900D_Hardware Design_V1.04 7 2010.10.09

SIM900D Hardware Design
1 Introduction
This document describes the hardware interface of the SIMCom SIM900D module that connects to the specific
application and the air interface. As SIM900D can be integrated into a wide range of applications, all functional
components of SIM900D are described in great detail.
This document can help usres quickly understand SIM900D interface specifications, electrical and mechanical
details. With the help of this document and other SIM900D application notes, user guide, users can use SIM900D
module to design and set-up mobile applications quickly.
1.1 Related Documents
Table1: Related documents
SN Document name Remark
[1] SIM900_ATC SIM900_ATC
[2] ITU-T Draft new
recommendation
V.25ter:
Serial asynchronous automatic dialing and control
[3] GSM 07.07: Digital cellular telecommunications (Phase 2+); AT command set for GSM
Mobile Equipment (ME)
[4] GSM 07.10: Support GSM 07.10 multiplexing protocol
[5] GSM 07.05: Digital cellular telecommunications (Phase 2+); Use of Data Terminal
Equipment – Data Circuit terminating Equipment (DTE – DCE) interface for
Short Message Service (SMS) and Cell Broadcast Service (CBS)
[6] GSM 11.14: Digital cellular telecommunications system (Phase 2+); Specification of the SIM
Application Toolkit for the Subscriber Identity Module – Mobile Equipment
(SIM – ME) interface
[7] GSM 11.11: Digital cellular telecommunications system (Phase 2+); Specification of the
Subscriber Identity Module – Mobile Equipment (SIM – ME) interface
[8] GSM 03.38: Digital cellular telecommunications system (Phase 2+); Alphabets and
language-specific information
[9] GSM 11.10 Digital cellular telecommunications system (Phase 2)；Mobile Station (MS)
conformance specification；Part 1: Conformance specification
[10] AN_Serial Port AN_Serial Port
1.2 Terms andAbbreviations
Table2: Terms and Abbreviations
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Abbreviation Description
ADC Analog-to-Digital Converter
AMR Adaptive Multi-Rate
ARP Antenna Reference Point
ASIC Application Specific Integrated Circuit
BER Bit Error Rate
BTS Base Transceiver Station
CHAP Challenge Handshake Authentication Protocol
CS Coding Scheme
CSD Circuit Switched Data
CTS Clear to Send
DAC Digital-to-Analog Converter
DRX Discontinuous Reception
DSP Digital Signal Processor
DTE Data Terminal Equipment (typically computer, terminal, printer)
DTR Data Terminal Ready
DTX Discontinuous Transmission
EFR Enhanced Full Rate
EGSM Enhanced GSM
EMC Electromagnetic Compatibility
ESD Electrostatic Discharge
ETS European Telecommunication Standard
FCC Federal Communications Commission (U.S.)
FDMA Frequency Division Multiple Access
FR Full Rate
GMSK Gaussian Minimum Shift Keying
GPRS General Packet Radio Service
GSM Global Standard for Mobile Communications
HR Half Rate
I/O Input/Output
IC Integrated Circuit
IMEI International Mobile Equipment Identity
kbps Kilo bits per second
LED Light Emitting Diode
DDLO Deep Discharge Lock Out
Li-Ion Lithium-Ion
MO Mobile Originated
MS Mobile Station (GSM engine), also referred to as TE
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Abbreviation Description
MT Mobile Terminated
PAP Password Authentication Protocol
PBCCH Packet Switched Broadcast Control Channel
PCB Printed Circuit Board
PCS Personal Communication System, also referred to as GSM 1900
PDU Protocol Data Unit
PPP Point-to-point protocol
RF Radio Frequency
RMS Root Mean Square (value)
RTC Real Time Clock
RX Receive Direction
SIM Subscriber Identification Module
SMS Short Message Service
TDMA Time Division Multiple Access
TE Terminal Equipment, also referred to as DTE
THD Total Harmonic Distortion
TX Transmit Direction
UART Universal Asynchronous Receiver & Transmitter
URC Unsolicited Result Code
USSD Unstructured Supplementary Service Data
UVLO Under Voltage Lock Out
VSWR Voltage Standing Wave Ratio
Vmax Maximum Voltage Value
Vnorm Normal Voltage Value
Vmin Minimum Voltage Value
VIHmax Maximum Input High Level Voltage Value
VIHmin Minimum Input High Level Voltage Value
VILmax Maximum Input Low Level Voltage Value
VILmin Minimum Input Low Level Voltage Value
VImax Absolute Maximum Input Voltage Value
VImin Absolute Minimum Input Voltage Value
VOHmax Maximum Output High Level Voltage Value
VOHmin Minimum Output High Level Voltage Value
VOLmax Maximum Output Low Level Voltage Value
VOLmin Minimum Output Low Level Voltage Value
Inorm Normal Current
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SIM900D Hardware Design
Abbreviation Description
Imax Maximum Load Current
Phonebook abbreviations
FD SIM fix dialing phonebook
LD SIM last dialing phonebook (list of numbers most recently dialed)
MC Mobile Equipment list of unanswered MT calls (missed calls)
ON SIM (or ME) own numbers (MSISDNs) list
RC Mobile Equipment list of received calls
SM SIM phonebook
NC Not connect
1.3 Safety Precautions
The following safety precautions must be observed during all phases of the operation. Usage, service or repair of
any cellular terminal or mobile incorporating SIM900D modules, manufactures of the cellular terminal should
send words of the following safety information to users and operating personnels and to incorporate these
guidelines into all manuals supplied with the product. If not so, SIMCom does not take any liability for customer
failure to comply with these precautions.
Observe the restrictions of the usage of mobiles in a hospital or other health care facility. Switch
the cellular terminal or mobile off, since medical equipment may be sensitive not to operate
normally for RF energy interference.
Switch off the cellular terminal or mobile before boarding an aircraft. Make sure it is switched
off. The operation of wireless appliances in an aircraft is forbidden to prevent interference with
communication systems. Forget to think of these instructions may lead to the flight safety or
offending local legal action, or both.
Do not operate the cellular terminal or mobile in the presence of flammable gases or fumes.
Switch off the cellular terminal near petrol stations, fuel depots, chemical plants or where
blasting operations are in progress. Operation of any electrical equipment in potentially
explosive atmospheres can constitute a safety hazard.
Cellular terminal or mobile handset receives and transmits radio frequency energy while they are
switched on. RF interference can occur if it is used near TV sets, radios, computers or other
electric equipment.
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Road safety comes first! Do not use a hand-held cellular terminal or mobile when driving a
vehicle, unless it is securely mounted in a holder for hands free operation. Before making a call
with a hand-held terminal or mobile, park the vehicle.
GSM cellular terminals or mobiles operate over radio frequency signals and cellular networks
and cannot be guaranteed to connect in all conditions, for example no mobile fee available or
with an invalid SIM card. While users are in this kind of condition and need emergent help,
please remember using emergency calls. In order to make or receive calls, the cellular terminal
or mobile must be switched on and in a service area with adequate cellular signal strength.
Some networks do not allow for emergency call if certain network services or phone features
are in use (e.g. lock functions, fixed dialing etc.). User may have to deactivate those features
before user can make an emergency call.
Also, some networks require a valid SIM card to be properly inserted into the cellular terminal
or mobile.

SIM900D Hardware Design
2 SIM900D Overview
Designed for global market, SIM900D is a quad-band GSM/GPRS engine that works on frequencies GSM
850MHz, EGSM 900MHz, DCS 1800MHz and PCS 1900MHz. SIM900D features GPRS multi-slot class 10/
class 8 (optional) and supports the GPRS coding schemes CS-1, CS-2, CS-3 and CS-4.
With a tiny configuration of 33mm x 33mm x 3mm, SIM900D can meet almost all the space requirements in your
applications, such as M2M, smart phone, PDA, FWP, and other mobile devices.
The physical interface to the mobile application is a 48-pin SMT pad, which provides all hardware interfaces
between the module and customers’ boards.
zSerial port and Debug port can help user easily develop user’s applications.
zThe charge interface is very suitable for the battery power application.
zTwo audio channels including two microphone inputs and two speakers’ outputs can be easily built into
handset, headset and handfree channel.
zThe SPI display interface and two Programmable General Purpose Input & Output will give users the
flexibility to develop customized applications.
SIM900D is designed with power saving technique so that the current consumption is as low as 1.2mA in SLEEP
mode.
SIM900D is integrated with the TCP/IP protocol. Extended TCP/IP AT commands are developed for customers to
use TCP/IP protocol easily, which is very useful for data transfer applications.
The modules complied with RoHS directive 2002/95/EC
2.1 SIM900D Key Features
Table3: SIM900D key features
Feature Implementation
Power supply Single supply voltage 3.2V – 4.8V
Power saving Typical power consumption in SLEEP mode is 1.5mA ( BS-PA-MFRMS=2 )
Frequency Bands zSIM900D Quad-band: GSM 850, EGSM 900, DCS 1800, PCS 1900. The
SIM900D can search the 4 frequency bands automatically. The frequency
bands also can be set by AT command.
zCompliant to GSM Phase 2/2+
GSM class Small MS
Transmitting power zClass 4 (2W) at GSM 850 and EGSM 900
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zClass 1 (1W) at DCS 1800 and PCS 1900
GPRS connectivity zGPRS multi-slot class 10 （default）
zGPRS multi-slot class 8 (option)
zGPRS mobile station class B
Temperature range zNormal operation: -30°C to +80°C
zRestricted operation: -40°C to -30°C and +80 °C to +85°C(1)
zStorage temperature -45°C to +90°C
DATA GPRS:
CSD:
zGPRS data downlink transfer: max. 85.6 kbps
zGPRS data uplink transfer: max. 42.8 kbps
zCoding scheme: CS-1, CS-2, CS-3 and CS-4
zSupports the protocols PAP (Password Authentication Protocol) usually used
for PPP connections.
zIntegrates the TCP/IP protocol.
zSupport Packet Switched Broadcast Control Channel (PBCCH)
zCSD transmission rates: 2.4, 4.8, 9.6, 14.4 kbps, non-transparent
zUnstructured Supplementary Services Data (USSD) support
SMS zMT, MO, CB, Text and PDU mode
zSMS storage: SIM card
FAX Group 3 Class 1
SIM interface Support SIM card: 1.8V, 3V
External antenna Antenna pad
Audio features Speech codec modes:
zHalf Rate (ETS 06.20)
zFull Rate (ETS 06.10)
zEnhanced Full Rate (ETS 06.50 / 06.60 / 06.80)
zAdaptive multi rate (AMR)
zEcho Cancellation
zNoise Suppression
Serial port and
Debug port
Serial Port:
z7-wire modem interface with status and control lines, unbalanced,
asynchronous.
z1.2kbps to 115.2kbps.
zSerial Port can be used for AT commands or data stream.
zSupports RTS/CTS hardware handshake and software ON/OFF flow control.
zMultiplex ability according to GSM 07.10 Multiplexer Protocol.
zAutobauding supports baud rate from 1200 bps to 57600bps.
Debug port:
z2-wire null modem interface DBG_TXD and DBG_RXD.
zCan be used for debugging and upgrading firmware.
Phonebook management Support phonebook types: SM, FD, LD, RC, ON, MC.
SIM Application Toolkit Support SAT class 3, GSM 11.14 Release 99
Real time clock Implemented
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SIM900D Hardware Design
Timer function Programmable via AT command
Physical characteristics Size: 33x 33 x 3 mm
Weight: 6.2g
Firmware upgrade Firmware upgradeable by debug port.
(1) SIM900D does work, but deviations from the GSM specification may occur.
Table4: Coding schemes and maximum net data rates over air interface
Coding scheme 1 Timeslot 2 Timeslot 4 Timeslot
CS-1: 9.05kbps 18.1kbps 36.2kbps
CS-2: 13.4kbps 26.8kbps 53.6kbps
CS-3: 15.6kbps 31.2kbps 62.4kbps
CS-4: 21.4kbps 42.8kbps 85.6kbps
2.2 SIM900D Functional Diagram
The following figure shows a functional diagram of the SIM900D and illustrates the mainly functional part:
zThe GSM baseband engine
zFlash and SRAM
zThe GSM radio frequency part
zThe antenna interface
zThe Other interfaces
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Flash+SRAM
RF
Power Amplifier
26MHz
Transceiver
Analog
Controller
With PMU
Digital Baseband
RTC
Reset
I/Q
COL
POWER
32.768KHz
RF
interface
Battery
interface
ANTBattery
GPIO
Serial
Interface
GPIO
Serial Port
Digital interface
Debug/upgrading
program
SIM interface
LCD interface
PWRKEY
RTC Analog interface
Audio interface ADC Charger
Figure1: SIM900D functional diagram
2.3 SIM900D Evaluation Board
In order to help users with the application of SIM900D, SIMCom can supply an Evaluation Board (EVB) that
interfaces SIM900D directly with appropriate power supply, SIM card holder, RS232 serial port, handset port,
earphone port, antenna and all GPIO of the SIM900D.

SIM900D Hardware Design
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Figure2: Top view of SIM900D EVB
For details please refer to the SIM900D-EVB_UGD document.

SIM900D Hardware Design
3 Application Interface
SIM900D is equipped with a 48-pin SMT pad that connects to the cellular application platform. Sub-interfaces
included in these SMT pads are described in detail in following chapters:
zPower supply and charging control (please refer to Chapter 3.3 and 3.5)
zSerial interface and Debug interface (please refer to chapter3.9)
zTwo analog audio interfaces (please refer to Chapter 3.10)
zSIM interface (please refer to Chapter 3.11)
Electrical and mechanical characteristics of the SMT pad are specified in Chapter 5.
3.1 SIM900D Pin Description
Table5: Pin description
Power Supply
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
VBAT I 2 VBAT pins are dedicated to
connect the supply voltage.
The power supply of
SIM900D has to be a single
voltage source of VBAT=
3.2V...4.8V. It must be able
to provide sufficient current
in a transmit burst which
typically rises to 2A
Vmax= 4.8V
Vmin=3.2V
Vnorm=4.0V
VRTC I/O Current input for RTC when
the battery is not supplied for
the system.
Current output for backup
battery when the main
battery is present and the
backup battery is in low
voltage state.
Vmax=3.15V
Vmin=2.0V
Vnorm=3.0V
Iout(max)= 200uA
Iin= 3uA
Do not keep pin
open, it should
be connected to
a battery or a
capacitor.
VCHG I Voltage input for the charge
circuit, as the signal to detect
the charger insertion。
Vmax=7.5V
Vmin=4.5V
Vnorm=5.0V
If unused keep
open.
GND Ground
Power on or power off
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SIM900D Hardware Design
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS
PWRKEY I Voltage input for PWRKEY.
PWRKEY should be pulled
low to power on or power off
the system. The user should
drive the PWRKEY to low
level voltage for a short time
when power on or power off
the system because the
system need margin time in
order to assert the software.
VILmax=1.2V
VIHmin=2.6V
VIHmax=3.3V
VILmin= 0V
It is already
pulled up
Audio interfaces
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
MIC1P
MIC1N
I Positive and negative voice
band input
Audio DC Characteristics refer to
chapter 3.10
If unused keep
open.
MIC2P
MIC2N
I Auxiliary positive and
negative voice band input
If unused keep
open.
SPK1P
SPK1N
O Positive and negative voice
band output
If unused keep
open.
SPK2P
SPK2N
O Auxiliary positive and
negative voice band output
If unused keep
open.
AGND Analog ground Separate ground
connection for
external audio
circuits.
If unused keep
open.
GERNERAL PURPOSE input/output
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
STATUS O Indicate status of module 's
working
If unused keep
open
NETLIGHT O Indicate status of module's
network
If unused keep
open
DISP_DATA I/O
DISP _CLK O
DISP _CS O
DISP _D/C O
Display interface If unused keep
open
GPO1 O Normal Output Port If unused keep
open
KBR0 I/O Normal Output/Input Port
VILmax=0.4V
VIHmin=2.4V
VILmin= 0V
VIHmax= 2.95
VOHmin= 2.7V
VOLmax=0.1V
VOHmax= 2.95V
VOLmin= 0V
KBR0 pin can
be configured as
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SIM900D Hardware Design
sim card present
detection pin,by
“AT+CSDT”, If
unused keep
open
Serial port
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
RXD I Receive data
TXD O Transmit data
RTS I Request to send
CTS O Clear to send
RI O Ring indicator
DCD O Data carry detect
DTR I Data terminal Ready
VILmax=0.4V
VIHmin=2.4V
VILmin= 0V
VIHmax= 3V
VOHmin= 2.7V
VOLmax=0.1V
VOHmax= 3V
VOLmin= 0V
1. DTR Pin has
been pulled up.
2. If RXD pin
not used, it
should be pulled
up to 3V
through a 10k
resistor.
3. Other unused
pins keep open.
Debug interface
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
DBG_TXD O
DBG_RXD I
Serial interface for
debugging and firmware
upgrade
VILmax=0.4V
VIHmin=2.4V
VILmin= 0V
VIHmax= 3V
VOHmin= 2.7V
VOLmax=0.1V
VOHmax= 3V
VOLmin= 0V
If unused keep
open.
SIM interface
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
SIM_VDD O Voltage supply for SIM card The voltage can be select by software
automatically either 1.8V or 3V
SIM_DATA I/O SIM data input/output
SIM_CLK O SIM clock
SIM_RST O SIM reset
VILmax=0.15 *SIM_VDD
VIHmin=0.85*SIM_VDD
VILmin= 0V
VIHmax= SIM_VDD
VOHmin= SIM_VDD-0.1V
VOLmax=0.1V
VOHmax= SIM_VDD
VOLmin= 0V
All signals of
SIM interface
are protected
against ESD
with a TVS
diode array.
ADC
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
ADC0 I General purpose analog to Input voltage range: 0V ~ 2.8V If unused keep
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