Siemens 6ES7138-4DF00-0AB0 Digital Input Module

Siemens 6ES7138-4DF00-0AB0 is a Serial Interface Module (1SI) designed for the ET 200S decentralized I/O system, providing a single serial port (RS-232/RS-422) to connect a host controller or peripheral device to the ET 200S bus. It supports ASCII and 3964(R) serial communication, enabling integration with older PLCs or instruments that exchange data using these protocols and serving as a bridge between the ET 200S network and non‑S7 serial devices. A closely related variant, 6ES7138-4DF01-0AB0, adds Modbus/USS support for alternative serial communication needs. This is a discontinued interface module in the ET 200S family, with Siemens documentation indicating an end‑of‑life status around October 1, 2011.