4.5 Connect I/O Expander
PiBot RJ12 expansion port on UART2
Power off before connecting or disconnecting the expander. Use a PiBot-compatible RJ12 cable and confirm the expander supply requirements. RJ12 pinouts from unrelated products are not interchangeable.
Connection
- Complete the controller checklist and the optional RJ12 test first.
- Power off both boards.
- Connect the expander to item 6 using the approved cable.
- Power on and confirm that the expander starts without communication errors.
YAML Channel
The supplied test YAML uses uart2 with TX GPIO.0, RX GPIO.35, 1,000,000 baud and 8N1, plus uart_channel2. Preserve these settings for PiBot accessories unless their documentation specifies another profile.
The OLED uses separate I2C pins (GPIO.13/14), so it may be used at the same time as the RJ12 expander.
One UART channel, one planned topology. Do not split the RJ12 cable to a pendant and expander unless the accessory system explicitly supports that bus arrangement. GPIO.0 is also a boot-strap pin; a faulty peripheral can prevent normal boot.
Acceptance check: the board cold-boots with the expander connected, inputs and outputs update reliably, and unplugging the expander with power off does not change base-controller operation.