It's a breakout board for F411 board (black pill) running grblHAL FW. It is compatible with the default black pill mapping.
Limits, step/dir outputs and probing are tested and work fine.
Limits and probing inputs (especially probing) enable a very convenient tool change procedure, when the only thing you have to do is to change the tool and click "cycle start".
Buttons, step enable and spindle enable also work, spindle PWM and auxiliary inputs/outputs are not tested.
The left part of the board is fully isolated from the right part, provided that two isolated power supplies are used.
There is no isolation between the MCU board and the outputs, but this is not a problem taking into account that all these outputs go either to optocouplers or relays.
NCI stands for Non-Connected Input, NCO is an output.
All outputs provide 12V, so be careful connecting step motor drivers without any current limiting circuit. Some drivers have just one resistor in series with the optocoupler LED, others have a bit more complex constant current circuits, like this:
Most of the drivers without the constant current circuit expect 5V input, so adding a resistor in series with the driver input would be a good solution. As an alternative, 5V power supply could be used for the output part.