Im just a nube so it took me a while to figure it out.
on the unitronix side assign a slave to one of the ports like this
on the python side read data with something like this
import modbus_tk
import modbus_tk.defines as cst
import modbus_tk.modbus as modbus
import modbus_tk.modbus_tcp as modbus_tcp
import logging
logger = modbus_tk.utils.create_logger("console", level=logging.DEBUG)
master = modbus_tcp.TcpMaster(host='172.21.2.183', port=20257, timeout_in_sec=5.0)
master.open
actual_bits = master.execute(slave=1, function_code=cst.READ_COILS, starting_address=1, quantity_of_x=2)
print("actual_bits =", actual_bits)
master.close
remember the slave number!
Hope this helps someone