Aaeon PCM-4894 User Manual page 29

You can connect an LED to indicate when the CPU card is on. Pin
1 of CN8 supplies power to the LED; Pin 3 is the ground.
You can use a switch (or a lock) to disable the keyboard. In this
state, the PC will not respond to any input. This is useful if you
do not want anyone to change or stop a running program. Simply
connect the switch between Pins 4 and 5. The pin assignments
appear in the following table:
Pin Function
1 LED Power (+5 V)
2 NC
3 GND
4 Keyboard lock
5 GND
Pin Function
1 Vcc
2 FIR_RX
3 IR_RX
4 GND
5 IR_TX
Chapter 2 Installation 23