CP5512 Transmission Rate Locked: STEP 7 Network Parameter Fix

Problem Overview

The Siemens CP 5512 (order number 6GK1551-2AA00) is a PCMCIA Type II communications card that connects a programming device (PG) or PC to a SIMATIC S7 PLC over MPI or PROFIBUS. The card is operated through the SIMATIC NET PC software and is exposed to STEP 7 (V5.x) or TIA Portal (V13 and later) as a network interface.

A common field issue: the transmission rate (baud rate) selection in the CP 5512 properties dialog appears disabled (greyed out) or refuses to save. The CP 5512 is detected by the operating system, the driver is loaded, but the user cannot change 187.5 kbps / 1.5 Mbps / 12 Mbps, or the value is overwritten on every restart of STEP 7. This blocks all subsequent online operations - download, upload, online diagnostics, and firmware update via SIMATIC Manager.

Affected Hardware and Software

The CP 5512 is a legacy product, superseded by the CP 5711 (USB) and CP 5611 / CP 5612 (PCIe). However, the card remains in service on many brownfield S7-300 / S7-400 stations, which is why the transmission-rate lock continues to surface in field service tickets.

Root Cause Analysis

The transmission rate on a CP 5512 is not a free-form user field - it is a project-bound parameter. STEP 7 enforces the value from one of two locations, in this priority order:

1. The PG/PC Station configuration inside the active STEP 7 project (highest priority when an S7 connection is active).
2. The Set PG/PC Interface assignment for the installed CP 5512 driver (applies when no project connection is opened).

If neither source can write a value, the dialog will display the active rate but disable editing. The most frequent field causes are:

• Partial / corrupt SIMATIC NET install. The base driver is loaded, but the SIMATIC NET runtime that exposes the CP 5512 to STEP 7 is missing or was installed from a non-full distribution disc. Transmission rate is set internally by the missing component and exposed read-only to STEP 7.
• License key missing or invalid. A licensed SIMATIC NET installation is required to expose the CP 5512 in STEP 7's online interface. Without a valid license, the Set PG/PC Interface shows the card but the property page is locked.
• PG/PC Station present in the STEP 7 project. When a project contains a configured PG/PC Station with a CP 5512, STEP 7 reads the baud rate from SIMATIC PC Station > CP 5512 > Properties > Interface. The user-level Set PG/PC Interface dialog cannot override an active project setting.
• Stale registry entry. The Windows registry key HKLM\SOFTWARE\Siemens\SIMATIC_NET\CP5512 (or the 64-bit mirror) holds the last-saved baud rate. If the install was rolled back, the value may point to a hardware profile that no longer exists.

Diagnostic Procedure

Run the checks in the order shown. Each step isolates one of the four root causes above before a reinstall is attempted.

1. Verify the card is enumerated. Open Windows Device Manager. The CP 5512 must appear under PCMCIA adapters (or Network adapters on 64-bit systems) without a yellow exclamation. Note the Hardware Ids; they must include PCI\VEN_10B5&DEV_9050 or the Siemens-specific SIEMENS_CP5512 string.
2. Verify the SIMATIC NET service is running. Open services.msc and confirm SIMATIC NET Configuration Service and S7DOS Help Service are Started and set to Automatic.
3. Open Set PG/PC Interface. From SIMATIC Manager, select Options > Set PG/PC Interface. Choose the entry: PC internal / PC Card (MPI) <Active> or PC internal / PC Card (PROFIBUS) <Active>. Click Properties. Note whether the Transmission or Baud rate drop-down is greyed out.
4. Inspect the STEP 7 project. In SIMATIC Manager, right-click the project and select Open Object > PG/PC Station. If a station exists, open it and double-click the CP 5512 icon. The Interface tab contains the active baud rate. STEP 7 will use this value and lock the user-level dialog as long as the project is open.
5. Check the registry override. With admin rights, examine HKLM\SOFTWARE\Siemens\SIMATIC_NET\CP5512\Parameters on 32-bit Windows or the 64-bit equivalent. The value BaudRate should match the dialog. A value of 0 or FFFFFFFF indicates a corrupt profile.

Resolution Paths

Path A - Remove a PG/PC Station from the project (most common)

If the user-level Set PG/PC Interface cannot change the rate but the project's PG/PC Station can, STEP 7 is reading the project value.

1. Close SIMATIC Manager.
2. In Windows Explorer, open the project folder and delete or rename the subfolder containing the PG/PC Station (typically PG_PC or the file *.s7pgpc). Make a backup first.
3. Re-open the project. Set PG/PC Interface is now authoritative.
4. Open Set PG/PC Interface > Properties and set the transmission rate to the value required by the target MPI/PROFIBUS network. The standard MPI rate for S7-300/400 is 187.5 kbps; PROFIBUS DP is typically 1.5 Mbps for standard cabling or up to 12 Mbps for short segments.
5. Click OK and confirm with Accessible Nodes (PLC > Accessible Nodes) that the target CPU is found.

Path B - Repair the SIMATIC NET install (license / partial install)

If the dialog stays greyed out even with no project open, the SIMATIC NET installation is incomplete or unlicensed.

1. Open Control Panel > Programs and Features and note the SIMATIC NET version (for example SIMATIC NET PC Software V14 SP1).
2. Insert the original full-version DVD. Run Setup.exe and select Modify / Repair. Allow the installer to re-register the CP 5512 driver (S7cp551x) and the COM/LMS subsystem.
3. Apply the license key from the supplied *.zip or the Automation License Manager.
4. Reboot. Re-open Set PG/PC Interface > Properties; the transmission rate drop-down should now be active.

Path C - Field workaround when only one working disc is available

Operators with mixed install media (one full disc, one limited disc) can apply a two-step workaround that forces a non-volatile baud rate into the CP 5512 profile.

1. Install SIMATIC NET from the full disc and set the desired transmission rate in Set PG/PC Interface.
2. Confirm the rate is reachable: PLC > Accessible Nodes must list the S7 CPU.
3. Close SIMATIC Manager. Uninstall the full disc via Control Panel while leaving the driver files in place (use Modify, not Remove).
4. Install the limited disc on top. The previously written baud rate is retained in the registry and the CP 5512 will continue to come up at the configured rate, even though the dialog remains read-only.

Path D - Clean registry reinitialization

1. Back up the registry. Open regedit as Administrator.
2. Export HKLM\SOFTWARE\Siemens\SIMATIC_NET to a .reg file.
3. Delete the CP5512 subkey and any CP5512x entries under ...\Drivers.
4. Reboot. Reinstall the SIMATIC NET driver from the full DVD using the Add CP 5512 option in the SIMATIC NET setup wizard.
5. Reboot again. Re-open Set PG/PC Interface; the transmission rate is now editable and the default is 187.5 kbps for MPI.

Network Parameter Configuration in TIA Portal

For stations that have been migrated to TIA Portal (V13 or later) but still use a CP 5512 on the engineering side, the transmission rate is exposed through the Devices & Networks editor. According to the official TIA Portal documentation, network parameters identify the network within the system configuration - for example, the network name - while interface parameters define the specific transmission properties of a port.

1. In the TIA Portal project tree, open Devices & Networks.
2. Select the Network view tab and click the MPI/PROFIBUS subnet to which the CP 5512 is assigned.
3. In the inspector window under Properties > General, review the Network name and the Subnet type.
4. Select the CP 5512 port symbol. Under Properties > Interface, set Transmission rate to the required value.
5. Compile the project (hardware) and download the PC station configuration to the local PC station runtime.

Reference: Checking or changing network parameters and interface parameters (TIA Portal V20 documentation).

Standard Transmission Rate Reference

Verify the configured rate against the connected S7 CPU's MPI/PROFIBUS interface. A rate mismatch will cause Accessible Nodes to time out and the CPU's SF (red) LED may blink if PROFIBUS is involved.

Verification

1. Open SIMATIC Manager. From the menu, select PLC > Accessible Nodes. The connected S7 CPU should appear with its MPI/PROFIBUS address (for example MPIschnittstelle at address 2).
2. If the CPU does not appear, verify the physical bus termination is in place (connector with switch ON at both ends of the segment) and that the cable does not exceed the length allowed for the configured rate.
3. Once Accessible Nodes lists the CPU, open the project and download a small test block to confirm online operation.
4. Close and reopen SIMATIC Manager. The configured baud rate must persist - this confirms the registry write was successful and is not being overwritten on startup.

Troubleshooting Matrix

Migration Path to CP 5711 / CP 5611 A2

When the CP 5512 host PC is replaced - typical for Windows 10 / 11 rollouts - the PCMCIA socket is no longer present. The supported replacements are:

• CP 5711 (USB, 6GK1571-1AA00): functional equivalent for MPI and PROFIBUS at up to 12 Mbps. Uses the same SIMATIC NET driver family.
• CP 5611 A2 (PCIe, 6GK1561-1AA01) or CP 5612 (6GK1561-2AA00): preferred for fixed engineering stations and PROFIBUS DP master use.

When migrating, the project baud rate is preserved in the Set PG/PC Interface profile, but the physical interface changes. Run PLC > Accessible Nodes with the new hardware before opening the project to confirm the bus is healthy.

FAQ