Connecting CP 343-1 to SIMATIC C7-634 DP: Compatibility Guide

The SIMATIC C7-634 DP is a compact PLC + HMI combination that integrates a CPU 315-class controller with an OP operator panel in a single housing. Adding a CP 343-1 communications processor is the standard method to attach an S7-300-family controller to an Industrial Ethernet network for SCADA, MES, and PC-based HMI traffic. Because the C7-634 is a special form factor (not a rack-mounted S7-300), the compatibility of a CP 343-1 with the C7-634 DP must be verified against the C7 backplane, the CP firmware, and the STEP 7 hardware catalog before any integration begins. This reference walks through the verification, the configuration, and the field-proven pitfalls.

1. System Identification by MLFB

Every compatibility decision starts with the exact order number (MLFB) stamped on the device. Two MLFBs are involved in this integration:

1.1 Decoding the C7-634 DP MLFB (6ES7 634-2BF01-0AE3)

• 6ES7 — SIMATIC S7 product group.
• 634 — C7-634 family (C7-633/634 generation with CPU 315 class).
• 2 — Two communication interfaces in the integrated CPU.
• BF01 — Function variant: BF denotes PROFIBUS DP master interface on the first port. The trailing 01 is the hardware/firmware version.
• 0AE3 — Packaging, language, and certification suffix (German/English documentation, CE).

The C7-633/634 generation was the successor to the older C7-623/624 systems and bundles a CPU 315-class PLC with an OP7 or OP17 operator panel into one device. The integrated CPU provides a PROFIBUS DP master on the first MPI/DP port and a second MPI/DP port for additional networking. Reference: Siemens Support entry 4341304 — New SIMATIC C7-633 DP and C7-634 DP Control Systems.

1.2 Decoding the CP 343-1 MLFB (6GK7 343-1EX30-0XE0)

• 6GK7 — SIMATIC NET product group.
• 343 — CP 343-1 family for S7-300.
• 1 — Generation 1 form factor (single-width S7-300 module).
• EX30 — EX identifies the Lean variant; the trailing 30 is the hardware release (FW ≥ V3.0).
• 0XE0 — Packaging and certification (CE, RCM, KC, etc.).

The CP 343-1 Lean connects an S7-300 station to Industrial Ethernet and supports S7 communication, S5-compatible communication, PROFINET IO device (limited), and TCP/UDP open communication via the SEND/RECV and FETCH/WRITE services. Reference: CP 343-1 Lean manual (PDF) — Siemens Support.

2. C7-634 DP Backplane Architecture

The C7-634 is not a standard S7-300 rail. The integrated CPU exposes a fixed number of expansion slots on its internal backplane for adding function modules (FMs) and communications processors (CPs). Per the C7-633/634 product documentation, up to two CPs/FMs can be plugged into the C7-634 backplane alongside the integrated CPU. These slots are physically and electrically compatible with the standard S7-300 module bus, but they are housed inside the C7 enclosure.

3. CP 343-1 Lean Module Specification

Source: CP 343-1 Lean manual.

4. Compatibility Constraints for the C7-634 DP

Three independent constraints must be satisfied before the CP 343-1 can be commissioned in a C7-634 DP station:

4.1 Mechanical and electrical fit

The CP 343-1 is an S7-300 single-width module and physically fits the C7-634 expansion slot bus. The 40 mm module snaps onto the C7 internal rail and connects to the S7-300 backplane connector without adapters.

4.2 Slot count

The C7-634 DP allows up to 2 CP/FM modules. If the application already uses two module slots (e.g. a CP 343-1 plus a CP 340 serial, or two CP 343-1s), no third module can be added. Verify with the actual hardware configuration (HW Config) in STEP 7.

4.3 Firmware / STEP 7 catalog

The CP 343-1 EX30 (FW 3.0) requires an HSP or hardware catalog entry that is present in STEP 7 V5.5 + SP4 (or later) and in the TIA Portal as of V14 SP1. Older STEP 7 versions (V5.3, V5.4) require a Hardware Support Package (HSP) installed from the Siemens automation hotline. If the catalog entry is missing, the CP can be inserted mechanically but STEP 7 will reject the configuration at compile time with a hardware configuration error (OB 100 / OB 85 / SF LED on CP).

5. STEP 7 Version and Firmware Matrix

6. Configuration Procedure in STEP 7 V5.x

Use HW Config to insert the CP 343-1 in slot 4 (or 4 and 5) of the C7-634 station. The C7 occupies slot 3 (CPU) and slots 4–11 are available for I/O, FM, and CP modules. Place the CP in slot 4 unless the slot is already used by a function module.

1. Open SIMATIC Manager and load the S7 project containing the C7-634 station. If only the OP project exists, use PLC > Station Upload to PG to read the station.
2. Open HW Config. The C7-634 station should be shown with the CPU 315-2 DP in slot 3 and the integrated OP17 assigned to a free slot.
3. Open the SIMATIC 300 / CP 300 catalog. Locate CP 343-1 and select the exact order number 6GK7 343-1EX30-0XE0. If it is not present, install the HSP and refresh the catalog.
4. Drag the CP onto slot 4 of the rack. The Properties dialog opens automatically.
5. Assign an IP address to the Ethernet interface (e.g. 192.168.0.10, subnet 255.255.255.0). If a router is used, enter the router address. Do not use the same subnet as the MPI/DP network to keep broadcast domains clean.
6. Configure the S7 connection if you are using S7 communication. In NetPro, right-click the CP 343-1 and choose Insert New Connection. Select S7 connection, choose the partner (e.g. WinCC station or another S7-300/400), and assign a local connection ID.
7. Save and compile (Ctrl+S). STEP 7 validates the configuration; if the CP firmware is incompatible with the C7-634 CPU class, an error icon appears next to the CP slot.
8. Download the hardware configuration to the C7-634 CPU. Use PLC > Download. The C7-634 OP remains in run during the download; the CP will briefly lose its link during restart.
9. Confirm SF and BF LEDs on the CP 343-1 faceplate. SF should be off; BF should be off once the Ethernet cable is connected and the link partner is active.

7. Configuration Procedure in TIA Portal

1. Open the TIA Portal project and add a new device of type SIMATIC C7-634 DP (only available in V14 SP1 and later with the S7-300 HSP).
2. Open Device View on the C7 station. The C7 occupies slot 1 (PS), slot 2 (IM, if any), slot 3 (CPU 315-2 DP), slot 4+ (free).
3. From the hardware catalog, navigate to Communication modules > CP 343-1 and drag the 6GK7 343-1EX30-0XE0 onto slot 4.
4. In the inspector, set the IP address, subnet mask, and any PROFINET device name (only if PROFINET IO is used, which is not the case in the typical "read process data over Ethernet" application).
5. Compile and download to the C7 station.

8. Verification and Diagnostics

After download, run the following verification sequence:

8.1 Quick ping test from the PG

ping 192.168.0.10 -t

Reply from 192.168.0.10: bytes=32 time<1ms TTL=64
Reply from 192.168.0.10: bytes=32 time<1ms TTL=64

If the ping fails, the most common causes are: wrong subnet, switch port disabled, crossed/missing cable, or a duplicate IP address on the segment. Use Wireshark with a port mirror on the switch to confirm ARP requests from the CP.

9. Troubleshooting Matrix

10. S7 Connection Programming for Process Data

Typical use case from the source thread: a SCADA or MES station reads running time, downtime, production count, and fault flags from the C7-634 over Ethernet. The simplest implementation on the S7-300 side uses PUT/GET via the CP 343-1 (the Lean CP supports the S7 protocol server role for PUT/GET and FETCH/WRITE). The C7 program itself does not need to be changed — the CP exposes a transparent server interface.

10.1 Data block layout (example)

DATA_BLOCK "ProcessData"
  STRUCT
    runningTime   : DINT;   // seconds, increments in OB35
    downtime      : DINT;   // seconds
    goodCount     : DINT;   // good parts
    rejectCount   : DINT;   // rejected parts
    faultWord     : WORD;   // bit 0 = E-Stop, bit 1 = drive fault, etc.
    shiftNumber   : BYTE;   // 1, 2, 3
    spare         : BYTE;
  END_STRUCT;
END_DATA_BLOCK

The data block must be marked as non-optimized (i.e. retain the standard S7-300 absolute addressing) so that the PUT/GET partner can address it via byte offset. In STEP 7 V5.x this is the default for DBs. In TIA Portal, uncheck Optimized block access in the DB properties.

10.2 WinCC or third-party SCADA access

The WinCC station connects to the CP 343-1's S7 channel using the configured S7 connection. Tags map to offsets in DB100 (or whatever DB number is configured). Example tag list:

11. Alternative Communication Paths

If the CP 343-1 route is constrained (no slot available, CP firmware too old, or PROFINET IO controller needed), consider these alternatives:

• PROFINET via CP 343-1 (non-Lean, e.g. 6GK7 343-1EX21-0XE0): full PROFINET IO controller functionality. Higher cost.
• PROFINET via CP 343-1 Advanced (6GK7 343-1GX31-0XE0): adds web server, FTP, integrated switch, security functions.
• Use the integrated MPI/DP port for PROFIBUS DP: route the SCADA traffic via DP if a PROFIBUS-capable CP is available (e.g. CP 342-5).
• Replace the C7-634 with a C7-635 Key Panel / ET 200S + OP: for new builds, modern SIMATIC HMI panels (Comfort panels) and S7-1500 controllers provide native Ethernet without an external CP.

12. Field-Commissioning Checklist

1. Verify MLFBs on the device labels match the project: 6ES7 634-2BF01-0AE3 and 6GK7 343-1EX30-0XE0.
2. Confirm CP 343-1 is seated in a free C7-634 backplane slot and the locking screw is engaged.
3. Check the STEP 7 version in SIMATIC Manager > Help > About and update HW catalog if needed.
4. Configure a unique IP address and subnet that does not conflict with the MPI/DP network.
5. Define at least one S7 connection in NetPro before compiling.
6. Download HW Config to the CPU, then download the program blocks separately.
7. Check SF, BF, and LINK LEDs on the CP faceplate.
8. Run a ping test from the PG.
9. Establish the S7 connection from the SCADA station and verify live tag updates.
10. Document the IP, subnet, MAC address, and the S7 connection resource IDs in the project documentation.