https://www.arduino.cc/reference/en
arduino web IDE

https://www.arduino.cc/en/ArduinoModbus/ArduinoModbus

avoiding the overflow when using millis

https://github.com/stephane/modbusino un mini modbus para Arduinos
https://github.com/vinmenn/Crc16 simple crc-16 library for Arduino

declarar funciones

Afpro A framing protocol arduino python con 16bit CRC

https://medium.com/@araffin/simple-and-robust-computer-arduino-serial-communication-f91b95596788