A lot of VFD's support RS485 control so you can control from Serial port or USB with appropriate converter
You can use MODBUS or VFDMOD (V\https://github.com/aekhv/vfdmod)
I'm told that VFDmod is easier to configure.
But ask me tomorrow as that is my task for the day.
IMHO Modbus2Hal is at least at easy to configure as VFDMOD and it supports more function codes (at least in master).
Updated documentation can be found here:
hansu.github.io/linuxcnc-doc/drivers/mb2hal.html
