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Smart Machine Smart Decision
Table 12: Status of the NETLIGHT pin
Status
SIM900-DS behavior
Off
SIM900-DS is not running
64ms On/ 800ms Off
SIM900-DS not registered the network
64ms On/ 3000ms Off
SIM900-DS registered to the network
64ms On/ 300ms Off
GPRS communication is established
A reference circuit is recommended in the following figure:
Figure33: Reference circuit of NETLIGHT
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
Default function
Default state
GPIO1
40
GPIO1
Output, pull down
GPIO2
41
GPIO2
Output, pull down
GPIO3
42
GPIO3
Output, pull down
GPIO4
43
GPIO4
Output, pull down
GPO1
44
GPO1
Output, pull down
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
34
2013-01-20