Resolving S7-400 CP 443-1 IT to Mitsubishi A1SH Ethernet Setup

1. Problem Overview

A common integration challenge is establishing Ethernet communication between a Siemens SIMATIC S7-400 station and a Mitsubishi MELSEC-A1SH station, where the Mitsubishi side is already operational but the Siemens side fails to establish the link. The typical hardware involved in the described configuration is:

• Siemens S7-400 rack: PS 407 4A power supply, CPU 414-2 (6ES7414-2XG03-0AB0, firmware V3.13), and CP 443-1 IT (6GK7443-1GX11-0XE0) on slot 4.
• Mitsubishi A1SH station: MELSEC-A1SH CPU with an A1SJ71E71-B5-S3 Ethernet interface module.

The root cause of "Siemens side does not work" with the Mitsubishi side already talking is almost always one of the following:

1. Wrong transport protocol selected (ISO-on-TCP/TCP/UDP) in STEP 7 NetPro.
2. Partner declared as S7 station rather than unspecified connection.
3. Mismatched port, TSAP, or IP address between the CP 443-1 IT and the A1SJ71E71-B5-S3.
4. CPU 414-2 V3.13 operating mode restrictions (CPU 414-2 is a non-`F` variant without `PN` in the part number; it requires the CP for Ethernet routing).
5. Missing SEND/RECV blocks in the S7-400 user program to drive the configured connection.

This article walks through the full configuration and commissioning sequence for the S7-400 side, the matching A1SJ71E71-B5-S3 setup, and the diagnostics required to bring the link up.

2. Hardware Identification

Verify the order numbers by reading the front-panel label of each module and cross-checking the SIMATIC S7-400 module manuals on the Siemens Industry Online Support portal: support.industry.siemens.com. The CPU 414-2 part number 6ES7414-2XG03-0AB0 is the third-generation (XG03) variant; firmware V3.13 supports standard S7 communication and CP routing.

3. Protocol Compatibility Analysis

Siemens S7-400 CP 443-1 IT and Mitsubishi A1SJ71E71-B5-S3 do not share a native application-layer protocol. The decision tree is therefore protocol-architecture-specific:

Recommended path: configure a TCP connection with an unspecified partner on the S7-400 side, open a passive (server) or active (client) socket on the A1SJ71E71-B5-S3, and exchange either raw data or MC-protocol frames from the S7-400 user program. For deterministic monitoring of the partner, use the Siemens AG_SEND / AG_RECV function blocks (FB 5 / FB 6 on S7-400) — see STEP 7 V5.x library "SIMATIC_NET_CP".

4. CP 443-1 IT Network Configuration (HW Config)

1. Open the S7-400 station in SIMATIC Manager with STEP 7 V5.5 or V5.6 (CPU 414-2 XG03 is supported by STEP 7 V5.4 SPx and later).
2. Open HW Config and confirm the CP 443-1 IT (6GK7443-1GX11-0XE0) is inserted in the rack at the slot specified in the actual hardware (the user has it on slot 4).
3. Double-click the CP to open Properties — Ethernet Interface.
4. Set the IP address (e.g., 192.168.0.10), Subnet mask (255.255.255.0), and optionally the Router address if the partner is on another subnet.
5. Switch to the Options tab of the CP and verify the firmware version reported matches the actual module (the CP 443-1 IT 6GK7443-1GX11-0XE0 ships with various firmware levels; consult the SIMATIC NET CP 443-1 IT Operating Instructions entry for the firmware-to-feature matrix).
6. Ensure that "Use CP as router for S7 communication" is enabled only if you need PG/OP routing through this CP; for raw TCP it is not required.

Compile and download the hardware configuration to the S7-400. Confirm the CP's SF LED is off and the LINK/RX/TX LEDs reflect cable activity.

5. CP 443-1 IT Connection Configuration (NetPro)

1. In SIMATIC Manager, double-click NetPro to open the network view.
2. Select the CP 443-1 IT in the S7-400 station. Right-click the connection row at the bottom of the editor and choose Insert New Connection.
3. In the connection wizard, set the Partner to "Unspecified" (this is the critical step that most users miss — selecting an S7-300/400 partner generates a S7 connection that the A1SJ71E71 cannot respond to).
4. Choose the Type as TCP connection. (If you require ISO-on-TCP and the Mitsubishi side truly speaks RFC 1006 — most A1SJ71E71 firmware does not — pick ISO-on-TCP connection instead; otherwise remain on TCP.)
5. Click Apply, then open the connection properties to verify and document the parameters listed in the table below.
6. Download the connection configuration to the S7-400. The CP stores it in its connection database; the configured ID and LADDR must be referenced from the user program.

The configured ID is shown in the lower pane of NetPro. The LADDR (logical base address) is taken from the CP's hardware address — typically W#16#03FF for the first CP 443-1 in the S7-400. Confirm the value by reading the CP's diagnostic buffer in STEP 7 (PLC → Module Information → Diagnostic Buffer).

6. Mitsubishi A1SJ71E71-B5-S3 Configuration (GX Developer)

1. Open the A1SH project in GX Developer (or migrate to GX Works 2/3 — the A1SH is supported as a "transitional" target in GX Works 2).
2. In Parameters → Network Parameters → Ethernet / MELSECNET set:

3. Switch to Open Settings (or Connection Settings) and configure one open for the S7-400 partner:

4. Write the parameters to the A1SH CPU and reset the A1SJ71E71-B5-S3. The module's RDY LED should be steady green within a few seconds after restart.
5. Confirm the port is listening using a Windows PC and telnet 192.168.0.20 5000; the connection should remain open until either side closes it.

For reference, the operating manual of the A1SJ71E71-B5-S3 (IB-66820 or later revision) is available on the Mitsubishi Electric FA Global Site: mitsubishielectric.com/fa/ (search the e-Manual for SH-080008 or "A1SJ71E71").

7. Programming the S7-400 (SEND/RECV FBs)

Once the connection exists in NetPro, the user program must drive it. Use the FBs from the STEP 7 standard library SIMATIC_NET_CP:

• FB 5 AG_SEND — sends a data block over a configured TCP/ISO connection.
• FB 6 AG_RECV — receives a data block from the same connection.

Example call in STL (or import into a LAD/FBD block):

// Call once per cycle to receive
CALL FB 6, DB 6
   ID       := 1                  // connection ID from NetPro
   LADDR    := W#16#03FF          // logical address of CP 443-1 IT
   RECV     := P#DB100.DBX0.0 BYTE 200  // receive area, 200 bytes
   NDR      := M 100.0            // new data received (1 cycle pulse)
   ERROR    := M 100.1            // error bit
   STATUS   := MW 102             // extended status/diagnostics
   LEN      := MW 104             // actual bytes received
;

// Trigger a send from FC 12 (cyclic or event-driven)
CALL FB 5, DB 5
   ID       := 1
   LADDR    := W#16#03FF
   SEND     := P#DB110.DBX0.0 BYTE 200  // send area, 200 bytes
   LEN      := 200                 // bytes to transmit
   DONE     := M 110.0
   ERROR    := M 110.1
   STATUS   := MW 112
;

For multi-block payloads larger than the configured buffer, the LEN parameter must equal the total number of bytes; AG_SEND/AG_RECV handle fragmentation internally up to the CP's maximum PDU size (typically 8192 bytes for ISO-on-TCP, up to 64 KB for TCP, see CP 443-1 manual for limits).

8. Status Codes & Diagnostics

For deeper diagnostics, read the CP's diagnostic buffer from STEP 7 (PLC → Module Information → Diagnostic Buffer → "Open"). The CP 443-1 IT (6GK7443-1GX11-0XE0) records connection states with text strings such as "Connection to partner x.x.x.x:port established" or "Connection terminated because of partner reset". If the buffer shows "no partner reachable" the issue is at the IP/routing layer; if it shows "connection aborted" the issue is at the A1SJ71E71 side.

9. Verification & Testing

1. Link check: Verify the Ethernet link LEDs on both the CP 443-1 IT and the A1SJ71E71-B5-S3 are lit for the connected port. The CP's LINK LED and the Mitsubishi's COM.ERR LED must both be off.
2. Ping test: From a PG/PC on the same subnet, ping 192.168.0.20 (A1SJ71E71) and ping 192.168.0.10 (CP 443-1 IT). If ping fails, the issue is purely Layer 3 — fix the IP/subnet/gateway first.
3. TCP socket test: With the A1SJ71E71 in MC-protocol Unpassive mode, connect using telnet 192.168.0.20 5000. The connection should remain open; type a few hex bytes and observe the A1SJ71E71's RDY LED for activity.
4. STEP 7 monitor: In NetPro, right-click the S7-400 CP and choose Connection Status (online). The configured TCP connection to the unspecified partner should show Established.
5. FB monitoring: In online mode, watch the STATUS output of AG_SEND / AG_RECV. STATUS = W#16#0000 (DONE/NDR = 1) indicates a successful transmission/reception cycle.
6. Loopback test: For first commissioning, configure the A1SJ71E71 to echo received bytes back to the sender (A1SJ71E71 has a built-in echo back / test function accessible through GX Developer → Diagnostics → Test). Use the S7-400 user program to send 16 bytes and compare them with the received buffer.

10. Troubleshooting Matrix

11. Cross-Reference: Where to Find Official Documentation

• Siemens S7-400 CPU 414-2 manual and firmware history: support.industry.siemens.com — CPU 414-2 manual (entry IDs change periodically; search "6ES7414-2XG03-0AB0").
• Siemens CP 443-1 IT (6GK7443-1GX11-0XE0) manual: support.industry.siemens.com — CP 443-1 IT Operating Instructions.
• Siemens STEP 7 V5.x manual collection, including NetPro: support.industry.siemens.com (entry ID 18652656 for the STEP 7 V5.5 manual set).
• Siemens function block library SIMATIC_NET_CP (FB 5, FB 6): bundled with STEP 7 V5.x; documentation in the online help of the SIMATIC Manager.
• Mitsubishi Electric FA documentation portal: mitsubishielectric.com/fa/ — search for the A1SJ71E71-B5-S3 user's manual (manual code SH-080008 or IB-66820).
• Independent HMI vendor connection guide (Weintek) confirming the parameter set for the S7-400 (IP, Port, Link type, Rack, CPU slot): Weintek S7-400 Ethernet Connection Guide (PDF).