# NullModem

Pymodbus offers a special NullModem transport to help end-to-end test without network.

The NullModem is activated by setting host= (port= for serial) to NULLMODEM_HOST (import pymodbus.transport)

The NullModem works with the normal transport types, and simply substitutes the physical connection: - Serial (RS-485) typically using a dongle - TCP - TLS - UDP

The NullModem is currently integrated in - `Modbus<x>Client` - `AsyncModbus<x>Client` - `Modbus<x>Server` - `AsyncModbus<x>Server`

Of course the NullModem requires that server and client(s) run in the same python instance.