Siemens Communication Module for ET 200S RS-232C RS-422 RS-485 MODBUS USS 6ES7138-4DF11-0AB0

Siemens Communication Module for ET 200S RS-232C RS-422 RS-485 MODBUS USS 6ES7138-4DF11-0AB0

Product Overview

Siemens 6ES7138-4DF11-0AB0 is an ET 200S electronics module that provides a single serial interface (SI) for industrial communication over standard asynchronous serial protocols. It is intended for use in the SIMATIC DP distributed I/O system, enabling connection of devices using RS-232C, RS-422 and RS-485 physical layers and supporting MODBUS and USS protocol stacks. The module integrates into an ET 200S station on a PROFIBUS DP or PROFINET backbone via an appropriate interface module, enabling PLCs to exchange serial data with remote field equipment efficiently over long distances.

Key Technical Specifications

Power & Electrical

• Supply voltage (L+): 24 V DC (rated)

• Reverse polarity protection: Yes

• Input current from L+: max. 80 mA (typical ~20 mA)

• Backplane bus current (3.3 V DC): max. 10 mA

• Typical power loss: 1.2 W

Communication Interface

• Number of interfaces: 1

• Serial support:

  • RS-232C (V.24): Full control signal set (TxD, RxD, RTS, CTS, DTR, DSR, DCD, PE)

  • RS-422: Differential transmit and receive (TxD(A/B), RxD(A/B), PE)

  • RS-485: Differential half-duplex (R/T(A/B), PE)

• Transmission rate (max): 115.2 kbit/s (supported half-duplex)

• Protocols supported:

  • MODBUS

  • USS (Universal Serial Synchronous/Asynchronous)

• Character framing:

  • Data bits: 8

  • Start/stop bits: 1 or 2 (USS only 1)

  • Parity: None, odd, even (even only for USI)

Data Handling

• Bytes per PLC cycle:

  • Transmit: up to 32 bytes (higher with specific IM151-1 couplers)

  • Receive: up to 32 bytes

Cable & Distance

• RS-232C cable length (shielded): max. 15 m

• RS-422/RS-485 cable length (shielded): max. ~1200 m

Diagnostics

• LED indicators:

  • RxD (receive activity)

  • TxD (transmit activity)

  • Group error (SF): Red fault indicator

• Galvanic isolation:

  • Between serial interfaces and internal power supply

Environmental & Physical

• Operating temperature: 0 °C to 60 °C

• Storage/transport temperature: −40 °C to 70 °C

• Dimensions:

  • Width: 15 mm

  • Height: 81 mm

  • Depth: 52 mm

• Weight: ~50 g

Functional Description

The 6ES7138-4DF11-0AB0 module is a single-channel serial communications interface designed to extend the functionality of the SIMATIC ET 200S I/O system by enabling connection and data exchange with devices that communicate over asynchronous serial protocols such as MODBUS and USS. It supports multiple physical interfaces (RS-232C, RS-422, RS-485) and is capable of handling typical industrial serial communication speeds up to 115.2 kbit/s, with adjustable framing and parity options for protocol flexibility.

This interface module is suitable for applications where remote field equipment—like sensor nodes, drives, or legacy instrumentation—uses standard serial comms and needs to integrate into a PLC-controlled system. The integrated diagnostics (RxD/TxD and error LED) provide basic health/status information to the control system.

Typical Use Cases

• Integrating serial field devices (Modbus sensors, USS field modules) into a PLC automation network

• Providing long-distance serial communication (up to ~1200 m with RS-422/485)

• Bridging legacy equipment into modern distributed I/O systems

• Capturing cyclic data for PLC logic through standard serial protocols

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