Add support for max485

[iosifnicolae2]

Description:

How to use it

Add the following lines to user_config_override.h:

#ifndef USE_MAX485
#define USE_MAX485
#endif

#ifndef MAX485_DE_PIN
// GPIO 0 = D3
#define MAX485_DE_PIN 0
#endif

Wiring

• MAX 485 DI -> ESP RX
• MAX 485 RO -> ESP TX
• MAX DE -> D3 (GPIO 0)
• MAX RE -> D3 (GPIO 0)

Related issue (if applicable):

• fixes smart meter interface with modbus and MAX485 wiring issue #10795
• fixes RS485 suport for modbus over MAX485 #7317

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works with Tasmota core ESP32 V.2.0.5 (I didn't tested it)
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass

[arendst]

Thx.

The solution resembles the software serial setTransmitEnablePin() function. Your implemntation adds a lot of code duplication AND compile time GPIO defines.

This won't be merged as is.

Considering the demand I will implement setTransmitEnablePin() in the smallest foodprint possible. Once implemented the calling driver will need to be changed for accessing the TransmitEnable GPIO.

[arendst]

Implemented in all generic tasmota drivers.

SML driver is a special project from @gemu2015 and uses a mix of TasmotaSerial, SoftwareSerial and hardware serial and currently does not support the new TasmotaSerial setTransmitEnablePin() feature.

This should be fixed by @gemu2015.

[nunojpg]

@arendst this is not working for me and after reviewing the code I don't think it can work at all with hardware ports, since the transmit enable pin stays up just for the time you take to queue the bytes, the transmission then is async.

[arendst]

Using latest Dev branches I can assure you it works as designed

[nunojpg]

@arendst using ESP32 (m_hardserial = true), then m_tx_enable_pin stays high for about 250us, while the bits then take much longer to come out from the hardware serial port.
I am sure it works fine with a soft serial port, but not with hardware serial port.
I am using 12.4.0.2.

[nunojpg]

SML implementation works because it correctly flush the fifo before disabling the TX EN pin.

[arendst]

Ok so I just need to add the flush on esp32 hardware serial before disabling.

[arendst]

Try latest dev and let me know if it fixes your issue.

[nunojpg]

Works great. Thanks for doing it so fast!