SIM900 Hardware Design
The power on scenarios illustrates as following figure.
STATUS
（OUTPUT）
V
IL
<0.15*VDD_EXT
V
IH
> 0.85*VDD_EXT
Pulldown >1s
VBAT
PWRKEY
(INPUT)
V
OH
> 0.85* VDD_ EXT
Serial Port Undefined
Active
Delay > 3.2s
Figure 8: Timing of turn on system using PWRKEY
When power on procedure completes, the SIM900 will send out following result code to indicate the module is
ready to operate when set as fixed baud rate.
RDY
This result code does not appear when autobauding is active.
3.4.1.2 Turn on SIM900 Using the PWRKEY Pin and PWRKEY_OUT Pin (Power on)
User can turn on SIM900 by connecting PWRKEY Pin and PWRKEY_OUT Pin for a short time and then
release. The simple circuit illustrates as the following figures.
Turn On/Off Impulse
PWRKEY_OUT
PWRKEY
MODULE
SIM900
100K
Figure 9: Turn on SIM900 using driving circuit
SIM900_HD_V1.05 06.23.2010
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