Do not have such a board. Here my assumptions.
The boards have an onboard CPU which either
- provides external RS485 access to the board's features
- or allows to use the RS485 transmitter from the host-RPi .
The access to the RS485 transmitter is controlled by the jumper settings.
The 'megaind' command is responsible to setup the board's own CPU with serial port configuration. Then the board CPU can respond to external modbus request. RPi is not involved in this setup.
The boards - when switched to RPi serial - use the RPi serial port and should be programmed with e.g. a python program and minimalmodbus.
You need an external modbus device which responds to the requests from RPi to see success.
Had a look to some of the schema of the boards and there are circuit which autogenerate the data-direction line of the RS485 transmitter's DI, RE/ signal. So no need to setup the RPI UART to use control lines.
Found some remarks on using the RS485 line in the Sequent forum.
The boards have an onboard CPU which either
- provides external RS485 access to the board's features
- or allows to use the RS485 transmitter from the host-RPi .
The access to the RS485 transmitter is controlled by the jumper settings.
The 'megaind' command is responsible to setup the board's own CPU with serial port configuration. Then the board CPU can respond to external modbus request. RPi is not involved in this setup.
The boards - when switched to RPi serial - use the RPi serial port and should be programmed with e.g. a python program and minimalmodbus.
You need an external modbus device which responds to the requests from RPi to see success.
Had a look to some of the schema of the boards and there are circuit which autogenerate the data-direction line of the RS485 transmitter's DI, RE/ signal. So no need to setup the RPI UART to use control lines.
Found some remarks on using the RS485 line in the Sequent forum.
Statistics: Posted by ghp — Mon Dec 08, 2025 11:45 am