You can do this by setting up PDO mapping in your EtherCAT config tool (like TwinCAT, Acontis, or whatever master you’re using).

Basically, in your setup:

SubDeviceA → Write output at bit 0 / Read input from bit 8 (datagram 0). SubDeviceB → Same but on datagram 1. You just need to manually assign bit offsets in the process image inside the config tool. Most of the time, you don’t need to mess with the ENI file unless your master doesn’t support bit-level mapping.