STEP7 v5.5 PCS7 v7.1 S7-300 Download Icon Missing via CP342-5

Problem Description

When an S7-300 station equipped with a CP 342-5 communications processor is integrated into a SIMATIC PCS 7 V7.1 multiproject and the Engineering Station (ES) is running STEP 7 V5.5, the download icon (the PLC target-system download shortcut in the LAD/FBD/STL editor and in the block folder) is no longer active for the S7-300 CPU. Under STEP 7 V5.4 SPx the same configuration, the same project structure, and the same CP 342-5 wiring still allow the engineer to select PLC → Download directly to the S7-300 target system.

The visible symptom is one of the following:

• The toolbar download button is grayed out while the S7-300 is shown online reachable in the Accessible Nodes dialog.
• Right-click context menu on the S7 Program node shows Download as unavailable.
• Selecting PLC → Compile and Download Objects reports Target system cannot be identified.
• The Target system / PG-PC assignment dialog (Menu Options → Set PG/PC Interface) lists the CP 342-5 as online-capable, but the project download is refused.

The root cause is the project-type classification of the master project inside the SIMATIC Manager, combined with the way PCS 7 V7.1 protects subordinate S7-300 stations that were inserted as STEP 7 subprojects. The project-type property "PCS 7" versus "STEP 7" controls which download mechanisms are exposed to the editor; in PCS 7 mode the S7-300 is treated as an AS (Automation Station) subordinate to the OS, and the classic single-station download path is suppressed.

Affected Software Versions

Per the official STEP 7 Compatibility List (Siemens Support, entry ID 109810730), STEP 7 V5.5 and V5.6 integrate the functionality of the PC-Adapter USB directly, so drivers no longer have to be installed manually to operate the adapter. The adapter detection is therefore not the cause of a missing download icon, but it is a frequent red herring during troubleshooting.

Root Cause Analysis

Two interacting mechanisms cause the missing download icon:

1. Project-type property in SIMATIC Manager. A PCS 7 multiproject is flagged with the Project type = PCS 7 attribute. Child stations that are pure S7-300 projects inserted into the multiproject inherit PCS 7 protection, and STEP 7 V5.5 enforces a stricter check on whether a single-station LAD/FBD/STL download is allowed. Under STEP 7 V5.4 the check was permissive; under V5.5 it returns download disabled unless the project type is changed to "STEP 7". The menu Project → Properties → Project type does not allow demotion from PCS 7 to STEP 7 in a multiproject that already has an AS-OS coupling.
2. NetPro connection topology for cross-station download. The ES does not download directly to the CP 342-5 over MPI/DP; it needs an S7 connection between the ES (the PG/PC in NetPro) and the S7-300 station. If the S7-300 lives in a separate STEP 7 subproject that is referenced from the PCS 7 multiproject, the connection must be created as an S7 connection across projects (cross-project S7 connection in NetPro). When that connection is missing, the Target system object of the S7-300 S7 Program node has no resolvable route, and the download shortcut is greyed out.

The combined effect is that the editor cannot resolve which S7-300 should receive the blocks because (a) the project type forbids single-station download inside a PCS 7 master, and (b) the cross-project S7 connection is not in place to give it an alternate route.

Diagnostic Procedure

1. Open SIMATIC Manager with the multiproject that contains the PCS 7 master and the S7-300 subproject.
2. Right-click the multiproject root → Properties. Confirm that Project type is PCS 7. Note that you cannot change it from here while AS-OS coupling exists.
3. Select the S7-300 station → Edit → Open Object on the S7 Program node. Open the LAD/FBD/STL editor on any block. Observe whether the download icon in the toolbar is greyed out.
4. Open Options → Set PG/PC Interface. Confirm the access point S7ONLINE is set to a usable adapter (e.g. PC-Adapter (Auto), TCP/IP → Broadcom NetXtreme ... for CP 443-1 routing, or the CP 5611 / CP 5621 PROFIBUS entry if the ES is on PROFIBUS).
5. Open Options → PG/PC Assignment for the S7-300 S7 Program node and check whether a target CPU is assigned. A blank assignment together with a greyed-out toolbar confirms the route is unresolved.
6. Open NetPro for the S7-300 subproject (Options → Configure Network). Check whether an S7 connection to the ES (or to the S7-400 AS that sits in the PCS 7 master) is configured. A missing or incomplete connection entry reproduces the symptom.
7. From a Windows command line on the ES, run ping <CP443-1 IP> and ping <CP342-5 routed IP> to confirm IP reachability through the S7-400 backplane (when the path is Industrial Ethernet on the OS side, PROFIBUS on the AS side).
8. Open PLC → Accessible Nodes on the S7-300 subproject. If the S7-300 CPU is listed with its PROFIBUS or Ethernet address, the physical layer is good and the problem is strictly project-side.

Solution A: Re-Structure the Multiproject

This is the solution recommended in the SIMATIC community knowledge base for sites that can separate the S7-300 and S7-400 control layers into different physical/logical projects. The S7-300 then becomes a normal STEP 7 project and the full download icon set is restored.

1. In SIMATIC Manager, select the multiproject → File → Multiproject → Adjust → Separate Project from Multiproject. Choose the S7-300 station (or the BHAS4Cent cluster of S7-300 PLCs) and confirm.
2. Open the separated project and verify Project → Properties → Project type shows STEP 7. If it still says PCS 7, demote the project type explicitly (this is only possible when the project has no AS-OS coupling artefacts and no CFC/SFC charts).
3. Re-insert the separated S7-300 project into a fresh STEP 7 multiproject that also contains the S7-400 master (Insert → Station → SIMATIC 300 Station). This keeps the S7-400 and S7-300 in the same multiproject without forcing the S7-300 to inherit PCS 7 properties.
4. Open NetPro and add an S7 connection from the S7-400 to the S7-300 (and from the ES PG to the S7-300). The connection type is S7 connection for MPI/PROFIBUS, and S7 connection (TCP/IP) when the ES reaches the S7-300 over the CP 443-1 routed path.
5. Compile NetPro (Network → Save and Compile). Download the connection configuration to the S7-400 first, then to the S7-300.
6. Open the LAD/FBD/STL editor on the S7-300. The download icon should now be active. Verify with PLC → Download.

Solution B: Keep the PCS 7 Master and Configure Cross-Project S7 Connections

When the S7-300 must remain inside the PCS 7 multiproject because the S7-300 and S7-400 exchange process data on a shared PROFIBUS segment (for example a shared DP slave such as an ET 200M, a SIMOCODE, or a SINAMICS drive), re-structuring is not an option. The supported path is to keep the multiproject structure and configure the connection correctly in NetPro.

1. In SIMATIC Manager, open the S7-300 subproject and the S7-400 subproject side by side.
2. Open NetPro for the S7-300 subproject (Options → Configure Network).
3. Right-click the CP 342-5 in the S7-300 station → Insert New Connection. In the connection dialog select the partner as (unspecified) and the connection type as S7 connection.
4. Open the partner's project (the PCS 7 master) in a second SIMATIC Manager instance. In the S7-400 station select the CP that is the physical gateway to the CP 342-5 (typically CP 443-1 for routed PROFINET → Industrial Ethernet, or the integrated DP interface of the S7-400 CPU if the path is direct PROFIBUS).
5. Return to the S7-300 NetPro, double-click the new S7 connection. Set the partner to point at the S7-400 CPU by entering its MPI, PROFIBUS, or IP address manually. Tick Establish an active connection if the S7-300 initiates the data exchange.
6. In the S7-400 NetPro confirm that the mirrored S7 connection appears on the CP 443-1 (or DP interface). Save and compile both NetPro instances.
7. Download the connection table to the S7-400 first, then to the S7-300.
8. Open the LAD/FBD/STL editor on the S7-300 blocks. The download icon will now resolve the target via the cross-project S7 connection.

Refer to chapter 10.8 Networking Stations from Different Projects of the SIMATIC Configuring Hardware and Communication Connections STEP 7 V5.5 manual (entry 18652656 on Siemens Support) for the official procedure. The same procedure is documented in the PCS 7 V7.1 manual PCS 7 Engineering System (entry 27013355).

Solution C: Demote the Project Type in Place (Use With Caution)

For stand-alone S7-300 stations that were inserted as STEP 7 subprojects into a PCS 7 multiproject and that have no AS-OS coupling and no CFC/SFC charts, the project type can be demoted. Do not use this procedure if the S7-300 contains PCS 7 library blocks, SFC instances, or if the OS references the S7-300 program for operator control and monitoring.

1. Open SIMATIC Manager with the S7-300 subproject.
2. Right-click the S7-300 project → Properties → Project type.
3. Change the project type from PCS 7 to STEP 7. Confirm the warning dialog.
4. Re-open the LAD/FBD/STL editor. The download icon is restored.

Verification

1. In the LAD/FBD/STL editor, open any block on the S7-300. The download icon in the toolbar is no longer greyed out.
2. Right-click the S7 Program → Download. The download dialog reports Download to target system completed without error.
3. Open PLC → Monitor/Modify on a known tag (e.g. DB100.DBD0) to confirm the online view is live.
4. Open PLC → Accessible Nodes. The S7-300 CPU is listed with the correct PROFIBUS or IP address, online status is green.
5. From the S7-400 station, perform a PLC → Download on a small modification to verify that the S7-300 ↔ S7-400 data exchange is not broken by the re-structure.

Related PC-Adapter USB Note (STEP 7 V5.5 / V5.6)

Per the official STEP 7 Compatibility List (Siemens Support, entry 109810730):

• The functionality of the PC-Adapter USB (6ES7 972-0CB20-0XA0) is integrated in STEP 7 V5.5 and V5.6.
• No separate driver install is required — Windows Plug-and-Plug enumerates the adapter and the S7ONLINE access point picks it up automatically.
• The PC-Adapter USB appears in Set PG/PC Interface as PC-Adapter (Auto), PC-Adapter (MPI), or PC-Adapter (PROFIBUS).
• USB-C and USB-A variants (6ES7 972-0CB35-0XA0) are supported on the same integrated driver in V5.5/V5.6.

If the download icon is missing but the adapter is recognised, the cause is project-side (Solutions A/B/C above) and not driver-side. A common field mistake is to install the legacy V5.4 PC-Adapter driver on a V5.5 ES, which collides with the integrated driver and can mask the CP 342-5 as reachable while the LAD/FBD/STL editor still refuses to download.

Troubleshooting Matrix

Field-Proven Caveats

• The CP 342-5 supports PROFIBUS-DP master and slave, not S7 communication in the same way as the integrated MPI/DP interface of an S7-300 CPU. The S7 connection used for download must be terminated on the CP 342-5 module, not on the CPU. Mis-targeting the S7 connection to the CPU MPI/DP interface is a common reason the editor cannot resolve the route.
• When the S7-300 sits behind an S7-400 (e.g. a CP 443-1 on the S7-400 side and a CP 342-5 on the S7-300 side with PROFIBUS between them), the ES download is a routed download. The S7ONLINE access point on the ES must be a TCP/IP access point that can reach the CP 443-1 first; the routed path is then resolved by the S7-400 acting as a router.
• PCS 7 V7.1 with STEP 7 V5.5 introduces a stricter integrity check on the AS-OS connection table. If the S7-300 subproject is not referenced by the OS server, the S7-300 can be safely extracted (Solution A). If the OS references the S7-300 program, use Solution B.
• STEP 7 V5.5 SP3 and later include a project-type sanity check that warns when the S7-300 subproject has CFC/SFC charts. Do not override the warning without removing the charts first.
• The STEP 7 V5.5 SP4 release notes (Siemens Support, entry 109810730) explicitly call out the change in download behaviour for S7-300 stations inside PCS 7 V7.1 multiprojects. The recommended migration path is the NetPro cross-project S7 connection procedure (Solution B above).

Edge Case: S7-300 with CP 343-1 (Ethernet Path)

If the S7-300 is fitted with a CP 343-1 (6GK7 343-1EX11-0XE0 or 6GK7 343-1CX10-0XE0) rather than a CP 342-5, the same symptom can occur, but the fix is simpler:

1. Add the CP 343-1 IP address to the ES as a reachable node in Accessible Nodes over TCP/IP.
2. In the S7-300 subproject, assign the S7ONLINE access point to the TCP/IP adapter pointing at the CP 343-1.
3. The download icon activates immediately — the project-type check is bypassed because the S7 connection terminates on the CP 343-1 directly.

This is the preferred path on greenfield projects. The CP 342-5 path in this article is specifically the legacy PROFIBUS route that surfaces the project-type bug.

Recommended Long-Term Architecture

For sites that have one S7-400 PCS 7 AS and several S7-300 satellite PLCs (e.g. centrifuge package PLCs, MCC PLCs, or skid PLCs from third-party OEMs), Siemens recommends the following:

• Keep the S7-400 in the PCS 7 master multiproject.
• Place each S7-300 in its own STEP 7 subproject and link the subprojects into the multiproject as STEP 7 projects (not PCS 7 projects).
• Use NetPro to create S7 connections from the S7-400 to each S7-300 over PROFIBUS or PROFINET.
• Expose the S7-300 tags to the PCS 7 OS via the S7-400 using Process Tags (PCS 7 V7.1+ supports indirect tag exposure through the AS).

This architecture avoids the project-type collision, gives each S7-300 an independent STEP 7 download path, and keeps the PCS 7 AS-OS coupling isolated to the S7-400.

FAQ