Notes:
The ? option allows reading back the current setting. The mode parameter allows specifying
how the GPIO1 pin will operate. The available modes are:
Analog, pin is internally disconnected and not used (default)
Input, low-to-high transition exits sleep mode
Input, high-to-low transition exits sleep mode
Output, low indicates messages pending for client (2)
Output, high indicates messages pending for client (2)
Output, low indicates in sleep mode (4). Otherwise output is high
Output, high indicates in sleep mode (4). Otherwise output is low
It is the responsibility of the client to provide pull-up resistors to the 3.3V supply rail. See the
reference design for resistor sizing. All output modes are open drain.
(1) - These two variations allow the user application to use GPIO1 as a general purpose output.
(2) - If either of these modes are selected, the pin will indicate if the Modem has received one or
more unread messages and is holding them for the client. If multiple messages are pending for
the client, the pin will maintain the state until all messages have been read.
(3) - GPIO will change states no faster than 500μs prior to the Modem beginning to transmit and
500μs after the Modem has finished transmitting.
(4) - If either of these modes are selected, the pin will be set to the selected state after the client
has issued the $SL command. The pin will return to the awake state only if the sleep mode is
terminated by the S or T parameter being reached, or activity is detected on the serial RX line.
November 2021 Swarm M138 Modem Manual - Rev 1.00 47/77
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