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README-GPIO.md

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X728-GPIOs and communication

Documentation from https://github.com/DavidAntliff/x728ups/blob/main/x728ups.py

GPIOs

GPIO 5 - "SHUTDOWN"

  • High > 600ms when UPS requests RPi shutdown
  • High > 200ms & < 600ms when UPS requests RPi reboot

GPIO 6 - "PLD"

  • AC power loss detection
  • High when external power is disconnected (and jumper 3 present)
  • Low when external power is connected (or jumper 3 is missing)

GPIO 12 - "BOOT OK"

  • RPi should set this high after boot
  • when the UPS is in shutdown-waiting mode, the RPi setting this to low initiates a UPS power-off after ~5300ms.

GPIO 13 - "BUTTON"

  • can be set by RPi for a period of time to simulate a button-press
  • therefore can initiate a shutdown sequence on the UPS

Protocol

RPi can request UPS shutdown with pulses on GPIO 13 UPS can request RPi shutdown with pulses on GPIO 5 UPS can notify RPi of external power status with GPIO 6 RPi can tell UPS that it is shut down with falling edge on GPIO 12 - UPS will auto-power off ~5300ms after this event.

Operation

Sequence of operation for this service is:

  1. User initiates RPi power up, or external power is restored and Jumper 2 (AON) is present.
  2. RPi boots and starts this systemd service (x728ups).
  3. This service sets GPIO 12 ("BOOT OK") high immediately.
  4. This service monitors GPIO 5:
    • If GPIO 5 is continuously high for more than 200ms and less than 600ms, this service will reboot the RPi.
    • if GPIO 5 is continuously high for more than 600ms, this service will shut down the RPi.
  5. This service monitors GPIO 6:
    • If GPIO 6 is continuously high for more than X seconds, this service will request a shut down of the system via GPIO 13 (see note below).

Note: System reboot (UPS & RPi) is requested by holding GPIO 13 high for 240 - 1500ms. System shutdown is requested by holding GPIO 13 high for longer than 1500ms. System immediate power-off occurs if GPIO 13 is high for longer than ~6400ms.

UPS states:

  • Idle mode - blue PWR LED is solid on.
  • ~200ms to ~1500ms button press results in ~500ms pulse on GPIO 5, triple-blink of blue PWR LED - request reboot.
  • ~1500ms or longer button press results in continual high on GPIO 5, pulsing of blue PWR LED - request shutdown.
  • If GPIO 12 does not go low shortly after either of these requests are issued, the mode expires after about 50 seconds.

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