SimCom SIM900D Hardware Design page 25

SIM900D Hardware Design
Turn on impulse
The power on scenarios illustrates as following figure.
VBAT
PWRKEY
( INPUT)
STATUS
（OUTPUT）
Serial Port
When power on procedure completes, the SIM900D will send out following result code to indicate the module is
ready to operate when set as fixed baud rate.
RDY
SIM900D_Hardware Design_V1.04
PWRKEY
4.7K
47K
Figure7: Turn on SIM900D using driving circuit
S1
PWRKEY
TVS1
Figure8: Turn on SIM900D using button
Pulldown >1s
V <0.15* VDD_ EXT
IL
Undefined
Figure9: Timing of turn on system using PWRKEY
3V
100K
Power on logic
MODULE
3V
100K
Power on logic
MODULE
Delay > 3.2s
V > 0.85* VDD_ EXT
IH
V > 0.85* VDD_ EXT
OH
25
Active
2010.10.09