25
25
Pinout and I/O Description
25
During the first seconds after powering up the module, these pins are in tristate. Use an
external pull-down or pull-up resistor to have the desired level during boot.
The GPx pins can drive a maximum current of 10mA.
4.11
LEDs
The LED pins can be used to monitor the module status. They can be used to drive
external LEDs. It is assumed that the LED lights up when the electrical level of the
corresponding pin is high. See also Appendix A.
Pin Name
Type
Level
Description
Comment
GPLED
O
3V3_LVTTL
First general purpose LED.
Max output current: 10 mA; output impedance: 20 Ohms
GPLED2
O
3V3_LVTTL
Second general purpose LED.
Max output current: 10 mA; output impedance: 20 Ohms
LOGLED
O
3V3_LVTTL
Internal logging status indicator.
Max output current: 10 mA; output impedance: 20 Ohms
During boot, i.e. during the first seconds after powering the module, the state of the LEDs
is not defined. Use a pull-down or pull-up resistor to force a desired state.
An example of a circuit with a 10k pull-down and a driver is shown below.
4.12
Standby
It is of course possible to power off the module by switching off the VDD_3V3 and VDD_BAT
supplies. However, this abrupt power interruption could cause data losses when logging
on an external SD card.
The module also supports standby mode, where it controls an external power switch and
turns itself off in a controlled way. This functionality involves the following pins:
Pin Name
Type
Level
Description
Comment
VDD_3V3
P,I
3.3V +/-5%
Main power supply input, controlled by the external power switch
All VDD_3V3 pins must be tied
together.
VDD_BAT
P,I
3.3V +/-5%
Always-on power supply, which must remain available when
VDD_3V3 is turned off by the external power switch
ONOFF
I, PU
3V3_LVTTL
Typically connected to a push-button to toggle between active
and standby mode. Toggling occurs when the ONOFF pin is driven
low for at least 50ms.
Internally debounced
