The Juice4halt Interface

The Juice4halt module uses the GPIO header of the Raspberry Pi for communication and for supplying the Raspberry Pi with power. Several pins are used. For some signals, it is possible to use an optional pin instead of the default pin when the default pin is already allocated by another task in your application. The change is done by removing/assembling a 0603-size jumper resistor on the determined positions. For further information see Application Note 171.

Pin1 (3V3)

is used for detecting if the Raspberry Pi is powered up. The GPIO25 (optional GPIO23) is
disconnected when the voltage at this pin falls to 0V.

Pin2 and Pin4 (5V)

5V backup power for Raspberry Pi

Pin22 (GPIO25) default
Pin16 (GPIO23) optional

3.3V logic signal for bidirectional Boot/Shutdown communication between the
Raspberry Pi and the Juice4halt. The Raspberry Pi reports the following states:

• Boot process completed
• Shut-down process completed

In the other direction, the Juice4halt forces the Raspberry Pi to shut down when the
charge state of the supercapacitors is too low

Pin15 (GPIO22) default
Pin11 (GPIO17) optional

An open-drain power failure signal output with 100k pull-up to 3.3V for an instant power
failure detection at the power input.

Pin3 (GPIO2/SDA)
Pin5 (GPIO3/SCL)

(only used in the RTC-485 model)
These two pins are used as the I2C interface for communication with the Real-Time Clock.

Pin8 (GPIO14/TXD)
Pin10 (GPIO15/RXD)

(only used in the RTC-485 model)
These two pins are used as the UART interface for the RS-485 communication.

Pins 6,9,14,20,25 (GND)

These pins are connected to ground.

All other pins are not occupied and can be used by other modules or HATs in the stack.