Support for RS485 on ESP32

[schotime]

nanoFramework area: (Hardware/target board | Community contributions)

Is your feature request related to a problem? Please describe.

RS485 is not fully supported on ESP32 hardware

Describe the solution you'd like

Implement the ability to handle different uart modes to support rs485 where the RTS pin needs to be set and hardware ctrl flow would also be disabled as per the spec: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/uart.html#communication-mode-selection

Describe alternatives you've considered

None

Additional context

Comments from @AdrianSoundy on Discord

For managed code i can't see an existing property to switch it to RS485 mode so a new one would need to be introduced, say "Mode" : Normal or RS485. If in RS485 mode all handshaking is disabled.
You would need to first update the Windows.Devices.SerialCommunication assembly which will create stubs to be used in the native code. Then using new stubs update native serial device to check mode property and set it in RS485 mode if required.

Submit a PR with the implementation

None yet.

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