Arduino Modbus library -Mega as Server using Serial ports 1,2 or 3 with RS485

Projects Interfacing w/ Software on the Computer
1

I want to use an Arduino Mega as a Modbus Server (slave) using the Tx1/Rx1 pins 18 and 19 and RE/DE pin >2 with my RS-485 hardware.

The ArduinoModbus.h library does not appear to provide for this option.

Is there another library which has this option?

2

According to posts on the Topic: Arduino Modbus Library the ArduinoModbus.h library is not suitable for the Uno/Mega.
Pylon posts
That library is designed for the MKR Arduino series. Don't use it on AVR type Arduinos (e.g. UNO, Mega2560, etc.).
Pylon also recommends that ModbusMaster.h from the IDE library be used instead.