Hardware Design V1.01(091226)
Table Of Contents
- Contents
- Version history
- 1 Introduction
- 2 SIM900 Overview
- 3 Application Interface
- 3.1 SIM900 Pin Description
- 3.2 Operating Modes
- 3.3 Power Supply
- 3.4 Power Up and Power Down Scenarios
- 3.5 Power Saving
- 3.6 Summary of State Transitions (except SLEEP mode)
- 3.7 RTC Backup
- 3.8 Serial Interfaces
- 3.9 Audio Interfaces
- 3.10 SIM Card Interface
- 3.11 LCD Display Interface
- 3.12 Keypad Interface
- 3.13 ADC
- 3.14 Behaviors of the RI
- 3.15 Network Status Indication
- 3.16 General Purpose Input Output (GPIO)
- 3.17 External Reset
- 3.18 PWM
- 3.19 I2C Bus
- 4 Antenna Interface
- 5 Electrical, Reliability and Radio Characteristics
- 6 Mechanics
SIM900 Hardware Design
Note: The AT command must be set after the SIM900 is power on and Unsolicited Result Code “RDY” is
received from the serial port. However if the SIM900 is set autobauding, the serial port will receive nothing.
The AT commands can be set after the SIM900 is power on. You can use AT+IPR=x;&W 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 Code “RDY” should be received from the serial port all the time that the SIM900 is power on. Please
refer to the chapter AT+IPR in document [1].
3.4.1.1 Turn on SIM900 Using the PWRKEY Pin (Power on)
You can turn on the SIM900 by driving the PWRKEY to a low level voltage with a limiting current resistor (1K
is recommended) in series for a short time and then release. This pin has pulled up to VDD_EXT in the module.
The maximum current that can be drained from the PWRKEY pin is 0.3mA. The simple circuit illustrates as the
following figures.
Figure 6: Turn on SIM900 using driving circuit
Figure 7: Turn on SIM900 using button
The power on scenarios illustrates as following figure.
SIM900_HD_V1.01 26.12.2009
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