SimCom SIM900 Hardware Design

SIM900 Hardware Design
3.4.2.1 Turn Off SIM900 Using the PWRKEY Pin (Power down)
You can turn off the SIM900 by driving the PWRKEY to a low level voltage for a short time and then release. You
also can urn off the SIM900 by connecting PWRKEY and PWRKEY_OUT for a short time and then release.
Please refer to the turn on circuit. The power down scenario illustrates as following figure.
This procedure lets the module 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 module will send out result code:
NORMAL POWER DOWN
After this moment, the AT commands can’t be executed. The module 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.
STATUS
（OUTPUT）
V
IL
<0.15*VDD_EXT
V
IH
> 0.85*VDD_EXT
5s > Pulldown >1s
PWRKEY
(INPUT)
V
OH
< 0.1V
Delay > 1.7s
Serial Port Undefined
Active
Logout net
Figure 12: Timing of turn off system using PWRKEY
STATUS
（OUTPUT）
5s > Impulse >1s
Turn Off Impulse
V
OH
< 0.1V
Delay > 1.7s
Serial Port Undefined
Active
Logout net
Figure 13: Timing of turn off system using PWRKEY and PWRKEY_OUT
SIM900_HD_V1.05 06.23.2010
27

SimCom SIM900 Specifications

General

Brand	SimCom
Model	SIM900
Category	Modem
Language	English