SIM900D Hardware Design
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47K
Turn on impulse
PWRKEY
Power on logic
100K
3V
MODULE
Figure7: Turn on SIM900D using driving circuit
S1
PWRKEY
TVS1
Power on logic
100K
3V
MODULE
Figure8: Turn on SIM900D using button
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
Figure9: Timing of turn on system using PWRKEY
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
2010.10.09
25
