Siemens 6ES7340-1CH02-0AE0 Communication Processor – CP 340

Siemens 6ES7340-1CH02-0AE0 CP 340 — RS422/RS485 Point-to-Point Communication Processor for SIMATIC S7-300

The 6ES7340-1CH02-0AE0 is a dedicated communication processor (CP) within the Siemens SIMATIC S7-300 modular PLC family. Its singular function is to manage autonomous point-to-point (PtP) serial data exchange over RS422 and RS485 physical layers, entirely independent of the S7-300 CPU’s scan cycle. This architectural separation is not incidental — it is the defining engineering rationale for deploying a CP module rather than relying on integrated CPU serial ports. In process-critical applications where deterministic CPU response time must be preserved, offloading serial I/O to the 6ES7340-1CH02-0AE0 eliminates the variable latency introduced by polling-based serial routines embedded in the main program organization block (OB1).

The module occupies a single slot on the S7-300 DIN rail assembly and draws power exclusively from the 5 VDC backplane bus at 160 mA — no external 24 VDC supply is required. Communication with the CPU occurs via the S7-300 internal P-bus (peripheral bus), using standard STEP 7 function blocks: FB 3 / FC 3 for transmit operations and FB 4 / FC 4 for receive operations. These driver blocks are freely available from Siemens Industry Online Support and integrate directly into the user program without requiring additional licensing.

The RS422/RS485 interface is electrically isolated from the backplane, providing galvanic separation between the serial field network and the PLC rack. This isolation is implemented via optocoupler-based signal conditioning on both transmit and receive paths, with a rated isolation voltage sufficient to withstand the common-mode transients typical of industrial cable runs in electrically noisy environments — motor drive cabinets, welding cells, and high-current switching gear. The RS485 half-duplex mode supports up to 32 nodes on a single bus segment at baud rates from 300 bps to 76.8 kbps. The RS422 full-duplex mode uses a 4-wire configuration (TX+, TX−, RX+, RX−) and supports cable runs up to 1,200 m at 9.6 kbps, making it suitable for distributed plant layouts where field devices are located far from the control cabinet.

Protocol support covers three modes: ASCII (free-format character framing), 3964(R) (block-oriented with acknowledgement handshake), and RK 512 (Siemens-proprietary record-based protocol for PLC-to-PLC data exchange). ASCII mode is the most flexible — it allows engineers to implement custom framing logic in STEP 7 to interface with virtually any third-party device that exposes a serial port, including barcode readers, weighing terminals, vision system controllers, servo drive parameter interfaces, and legacy SCADA RTUs. The 3964(R) protocol adds a defined STX/ETX block structure with BCC checksum and acknowledgement, reducing the application-layer error handling burden. RK 512 is used primarily for S7-300 to S5 legacy system migration scenarios.

From a hardware diagnostic standpoint, the module provides LED status indicators for power (SF/BF), transmit activity (TxD), and receive activity (RxD), enabling rapid visual fault isolation during commissioning and maintenance. Diagnostic data is accessible via the STEP 7 hardware diagnostics interface, including frame error counters, parity error counts, and buffer overflow events — all readable without interrupting ongoing communication.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

The 6ES7340-1CH02-0AE0 implements a dedicated microcontroller-based serial engine that operates independently of the S7-300 CPU’s main processor. This architecture means the CP 340 maintains its own transmit and receive buffers, manages baud rate clocking internally, and handles protocol framing (start bits, stop bits, parity, BCC checksum for 3964(R)) without consuming any CPU instruction cycles. The CPU interacts with the module only at the application data level — writing a data record to the CP’s P-bus address space to initiate a transmit, or reading a received data record after the CP signals completion via a status bit in the process image.

EMC Design: The RS422/RS485 driver circuitry uses differential signaling, which provides inherent common-mode noise rejection. In environments with high electromagnetic interference — variable frequency drives, contactors, inductive loads — differential pairs reject common-mode voltages up to the rated common-mode range of the RS485 standard (−7 V to +12 V). The galvanic isolation barrier (optocoupler stage) further prevents ground potential differences between the PLC cabinet ground and the field device ground from inducing error currents on the signal lines. Shielded twisted-pair cable with single-point shield grounding at the cabinet end is the recommended installation practice to maximize this EMC margin.

Receive Buffer Architecture: The CP 340 maintains an internal receive buffer that stores incoming serial data until the CPU reads it via the FB 4 / FC 4 receive function block. This decoupling means that even if the CPU is executing a time-consuming OB (e.g., a complex PID calculation or a large data block copy), incoming serial frames are not lost — they are held in the CP’s buffer. The buffer depth is sufficient for typical industrial message lengths; however, for high-throughput applications, the engineer must ensure the CPU read cycle is fast enough relative to the incoming message rate to prevent buffer overflow, which is flagged in the CP’s diagnostic data.

Slot Independence: Unlike some S7-300 special function modules that require specific rack positions, the CP 340 can be installed in any slot on the S7-300 rack (slots 4–11 on a standard rack). This flexibility simplifies rack layout planning, particularly in retrofit scenarios where an existing rack must accommodate an additional communication module without physical reconfiguration.

System Integration Benefits

• CPU Cycle Preservation: Serial communication is handled entirely by the CP’s onboard processor. The S7-300 CPU’s OB1 scan time is not extended by serial I/O wait states, maintaining deterministic PLC response times for time-critical control loops.
• Protocol Flexibility Without Custom Hardware: ASCII mode allows the engineer to define any framing structure in software (STEP 7 FB logic), eliminating the need for protocol converters or gateway hardware when integrating non-standard third-party devices.
• Long-Distance RS422 Reach: Full-duplex RS422 at 9.6 kbps supports cable runs to 1,200 m, enabling direct serial links to remote field instruments without signal repeaters or fiber-optic converters in many plant layouts.
• Multi-Drop RS485 Topology: Up to 32 devices on a single RS485 bus segment reduces wiring complexity and cabinet space compared to individual point-to-point connections for each field device.
• Galvanic Isolation for Ground Loop Prevention: The isolated interface eliminates ground loop currents that would otherwise corrupt serial data in plants where multiple grounding points exist across large physical distances.
• Integrated Diagnostic Transparency: Frame error counters, parity error statistics, and buffer status are accessible via STEP 7 hardware diagnostics without interrupting live communication, enabling predictive maintenance and rapid fault localization.
• No External Power Wiring: The module draws all operating power from the S7-300 backplane 5 VDC bus, eliminating the need for a separate 24 VDC terminal block connection and reducing wiring errors during installation.
• Slot-Independent Rack Placement: Installation in any available S7-300 slot (4–11) provides maximum flexibility for rack layout optimization in both new installations and retrofit expansions.
• Proven Field Longevity: The CP 340 family has been deployed in global manufacturing for over two decades. Replacement units remain essential for plant maintenance teams managing long-lifecycle S7-300 installations where system migration is not yet scheduled.
• STEP 7 Driver Block Availability: Siemens provides FB 3/FC 3 (send) and FB 4/FC 4 (receive) driver blocks as free downloads, reducing integration engineering time and ensuring standardized, documented communication logic.

Quality Assurance & Global Logistics

Every 6ES7340-1CH02-0AE0 unit supplied by siemensplc.com is sourced through verified industrial distribution channels with full traceability to Siemens-authorized supply chains. Each module undergoes a structured pre-dispatch inspection protocol:

• OEM packaging integrity check — Siemens label, hologram, and date-code verification against known-good references
• Visual inspection of PCB, connector pins, and housing for physical damage or signs of refurbishment
• Firmware version confirmation where applicable
• Functional power-on test with backplane bus communication verification
• Anti-static packaging with desiccant and humidity indicator card for moisture-sensitive electronics
• Full documentation package: commercial invoice, packing list, and certificate of origin for customs clearance

Dispatch is from our warehouse in Xiamen, China. In-stock units ship within 1–3 business days. International express freight (DHL, FedEx, UPS) delivers to most destinations within 3–7 business days. Air freight and sea freight options are available for volume orders. Export documentation complies with Chinese customs regulations and international trade requirements. T/T bank transfer, PayPal, and major credit cards are accepted.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
© 2026 siemensplc.com. All rights reserved.