SIM900D Hardware Design
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Turn on impulse
PWRKEY
Figure6: Turn on SIM900D using driving circuit
S1
PWRKEY
TVS1
Figure7: Turn on SIM900D using button
The power on scenarios illustrates as following figure.
STATUS
（
OUTPUT
）
V
IL
<1.2V
V
IH
> 2.6V
Pulldown >1s
VBAT
PWRKEY
(INPUT)
V
OH
> 2.7V
Delay > 2.2s
Serial Port
Undefined
Active
Figure8: 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
This result code does not appear when autobauding is active.
SIM900D_HD_V1.02
09.04.2010
25
