Так ведь было уже подобное:
https://support.wirenboard.com/t/problema-s-wb-mcm16-cherez-wb-mge/2853/6
Делаем примерно так
socat -d -d -d -x PTY,raw,ispeed=9600,ospeed=9600,parenb=0,cstopb=2,cs8,link=/dev/ttyRS485-x tcp:192.168.166.7:20108&
Далее модбас-клиентом опрашиваем созданный виртуальный порт
modbus_client --debug -mrtu -b9600 -pnone -s2 /dev/ttyRS485-x -a54 -t0x03 -r128 -c 1
Opening /dev/ttyRS485-x at 9600 bauds (N, 8, 2)
[36][03][00][80][00][01][81][A5]
2020/01/17 22:47:12.716984 length=8 from=0 to=7
36 03 00 80 00 01 81 a5
2020/01/17 22:47:12 socat[27492] I transferred 8 bytes from 5 to 7
Waiting for a confirmation…
< 2020/01/17 22:47:12.753129 length=7 from=0 to=6
36 03 02 00 36 cd 96
2020/01/17 22:47:12 socat[27492] I transferred 7 bytes from 7 to 5
<36><03><02><00><36><96>
SUCCESS: read 1 of elements:
Data: 0x0036