Specifications

AT Command Set Reference
Ver. 1.00
GSM1308AT001 Page 237 Ver. 1.00 – 10/29/2008
4.4.6 $IOPULUP GPIO Pullup Settings
(continued)
Examples
AT$IOPULUP?
$IOPULUP: 1x011111111100011111
GPIOs 3,13,14,15 have been set to
pulldonws and 1,4,5,6,7,8,9,10,11,12,
16,17,18,19,20 are set to pull-ups
AT$IOPULUP=11111111111100011111
ERROR
This command returns an ERROR because
it attempts to configure GPIO 3 as a pullup.