SIEMENS 6ES5944-7UB21 Communication Processor: Serial Connectivity for SIMATIC S5

In the architecture of industrial automation, reliable data communication between the programmable logic controller (PLC) and external devices is a cornerstone of integrated system functionality. The SIEMENS 6ES5944-7UB21, commercially designated as the CP 544, is a specialized communication processor engineered for the SIMATIC S5-115U, S5-135U, and S5-155U systems. This module extends the capabilities of the PLC beyond basic control by providing a robust serial interface, enabling point-to-point data links with a wide range of peripherals and systems. It serves as a dedicated communication channel, offloading data exchange tasks from the central CPU and ensuring reliable transmission for reporting, documentation, and peer-to-peer PLC links.

Core Functionality and Communication Role

The primary role of the CP 544 module is to manage serial communication according to established standards. It is equipped with a V.24 (RS-232) and TTY interface, selectable via a built-in DIP switch. This allows it to connect to devices using different voltage level standards. The module operates as an intelligent slave on the S5 backplane bus, handling protocol processing independently. It supports Siemens' proprietary 3964R procedure and the ASCII driver protocol, making it versatile for different communication needs. Its most notable capability is implementing the AS511 protocol, which is specifically designed for Siemens PLC serial communication, enabling reliable data block transfer between two S5 systems or to a programming device.

Key Technical Features and Design Benefits

• Dual Interface Support: Features both V.24 (RS-232-C) and TTY (20mA current loop) interfaces, providing compatibility with a broad spectrum of older and modern serial devices.

• Protocol Flexibility: Supports multiple transmission procedures including 3964R (rugged and error-correcting), ASCII driver for text-based communication, and the specialized AS511 protocol for Siemens-specific data exchange.

• Independent Processing: Contains its own processor and memory, handling communication tasks autonomously without burdening the central PLC CPU's cycle time.

• Comprehensive Parameterization: Configured via dedicated software (COM 544) or directly from the user program using function blocks (e.g., FB 244), allowing fine-tuning of baud rates, parity, data bits, and stop bits.

• Robust Diagnostic Capabilities: Extensive status and error information is available via LEDs on the front panel and can be read by the CPU program, facilitating quick troubleshooting.

• Industrial Hardening: Designed for the electrical noise and mechanical demands of industrial environments, ensuring stable communication even in challenging conditions.

Detailed Technical Specifications

Typical Industrial Applications

The SIEMENS 6ES5944-7UB21 finds its purpose in numerous automation scenarios requiring serial data interchange. A classic application is connecting a line printer or report printer to a PLC to generate shift reports, batch protocols, or alarm logs. In manufacturing cells, it can establish a data link between a main S5 controller and a subordinate controller handling a specific machine segment. It is also used to interface with serial terminal devices for manual data input or display. In process industries, it might connect to serial-output measuring instruments for logging values. Its robustness makes it ideal for these roles in environments like automotive plants, chemical processing, and material handling systems.

Configuration and Integration Notes

Integrating the CP 544 module requires careful planning. It occupies one slot in the S5 rack. Configuration is a critical step, typically performed offline using the COM 544 software to define parameters like the interface type (V.24/TTY), protocol, baud rate, and character format. These parameters are then transferred to the module. Alternatively, configuration can be done dynamically from the STEP 5 user program. Correct cable wiring is paramount; a standard null-modem cable is often insufficient. Siemens-specific cables or custom cables wired according to the selected interface (V.24 vs. TTY) and operational mode (DTE vs. DCE) are required for reliable operation. The module's address on the backplane bus must also be set correctly via coding switches.

Conclusion

The SIEMENS 6ES5944-7UB21 (CP 544) communication processor is a testament to the modular and extensible design of the SIMATIC S5 platform. By providing a dedicated, configurable serial communication channel, it enabled S5 systems to interact seamlessly with the wider world of industrial peripherals and data systems. Its support for robust protocols ensured reliable data exchange critical for documentation, coordination, and control.