I thought to write some description about my MODBUS MCU, but I think the video is better. So I did it (I don't speak English so good, but I can write subtitles).

Features in my Modbus slave controller:

• RS485 galvanic isolation (up to 560 Viorm).
• Work with modules DI8 (8 universal digital inputs) DO8 (8 digital outputs 3-28V) , DIO4 (4 universal universal digital inputs + digital outputs 3-28V), RLY4 (4 relay outputs), SSR4 (4 solid state relay with temperature protection).
• GPIOs can act as inputs or as outputs without reprogramming MCU.
• Ability to save outputs initial state.
• The best feature is the WATCHDOG implementation. If your main controller stuck, my MODBUS MCU return outputs in the initial state.

I also have RS485 radio extender and MODBUS RADIO module for wireless link up to 3 km. I will write about it later. Stay tuned)