General Purpose Input/Output (Gpio); External Reset - SIM Tech SIMCom SIM900-DS Hardware Design

Table 12: Status of the NETLIGHT pin
Status
Off
64ms On/ 800ms Off
64ms On/ 3000ms Off
64ms On/ 300ms Off
A reference circuit is recommended in the following figure:

4.13 General Purpose Input/Output (GPIO)

SIM900-DS provides up to 4 GPIO pins and 1 GPO pin. The output voltage level of the GPIO can be set by the
AT command "AT+ SGPIO". The input voltage level of the GPIO can also be read by the AT command "AT+
SGPIO". For more details, please refer to document [1].
Table 13: Pin definition of the GPIO interface
Pin name Pin number
GPIO1 40
GPIO2 41
GPIO3 42
GPIO4 43
GPO1 44

4.14 External Reset

The external NRESET pin is used to reset the module. This function is used as an emergency reset only when AT
command "AT+CPOWD=1" and the PWRKEY pin have no effect. The NRESET pin could be pulled down to
reset the module. The reset timing is illustrated in the following figure.
SIM900-DS_Hardware Design_V1.00
SIM900-DS behavior
SIM900-DS is not running
SIM900-DS not registered the network
SIM900-DS registered to the network
GPRS communication is established
Figure33: Reference circuit of NETLIGHT
Default function
GPIO1
GPIO2
GPIO3
GPIO4
GPO1
Smart Machine Smart Decision
Default state
Output, pull down
Output, pull down
Output, pull down
Output, pull down
Output, pull down
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2013-01-20