I am working on connecting an Omron E2B‑M12KN08‑M1‑C1 proximity sensor (NPN, NO) to the Digital Input of a RevPi MIO. The same sensor works correctly on a Horner PLC when wired directly, without any external pull‑up resistor. On the PLC, the signal reads HIGH (24 V) when the target is not detected and LOW (0 V) when detected.
However, the RevPi MIO does not detect the sensor output in the same configuration. I noticed the “Pullup” parameter in piCtory and set it to 1, but with this setting the input remains permanently HIGH (24 V), regardless of the sensor state.
The MIO schematic shows that the digital input uses a MAX22191 industrial input interface. According to the MAX22191 datasheet, the device should support both PNP and NPN proximity sensors. Despite this, the MIO input does not respond to the NPN sensor output.
I also tested the RevPi Connect 4 digital input and observed the same behavior: the NPN proximity sensor output is not detected.
This raises two questions:
1. Is an external pull‑up resistor (e.g., 4.7 kΩ to 24 V) required when using NPN sensors with the RevPi MIO or Connect 4 DI, even though other PLCs do not require one?
2. What exactly does the “Pullup” configuration option in the MIO settings do, and how is it intended to be used?
Any clarification or guidance would be greatly appreciated. Thank you.