chinesium relay board rs485 have data sheet with commands modbus rtu

www.alibaba.com/product-detail/Modbus-RT...e_1600958662317.html

I want to use this with Linuxcnc, I often need a lot of IO, typically not for anything super time critical RTAI. Just IO for doing random things. They offer these in 4 8 16 and 32 channel configurations. I also got them to kinda give me the entire protocol. So I am looking for a example modbus rtu protocol drive to look at to control these. They may have other useful modules as well. 

Maybe have a look at MB2HAL:

linuxcnc.org/docs/html/drivers/mb2hal.html

i'll pay someone I am super swamped and don't have time at the moment.