Overview
Connecting a Siemens S7-200 CPU to a PC running WinCC Flexible Runtime is a common engineering requirement, but the choice of the physical PC adapter determines whether the link comes up at all. Field experience has shown that the USB/PPI Multi-Master Cable (6ES7 901-3DB30-0XA0) is not supported by WinCC Flexible Runtime when targeting an S7-200. The supported path is the RS232/PPI Multi-Master Cable (6ES7 901-3CB30-0XA0), paired with a correct Set PG/PC Interface configuration and a single-channel WinCC connection of type MPI/DP.
This reference documents the working configuration for WinCC Flexible 2005 SP1 HF7 and WinCC Flexible 2007, the rationale for the cable selection, the exact PG/PC settings, and the commissioning checks that confirm a stable runtime link. The same cable and baud-rate rules apply when the HMI target is a TP177B panel acting as a second master on the PPI bus.
Affected Software and Firmware Versions
The compatibility constraint is anchored to the WinCC Flexible Runtime build, not to the S7-200 firmware. The versions encountered in production and training cells are listed below.
| Component | Version | Notes |
|---|---|---|
| WinCC Flexible Runtime | 2005 SP1 HF7 | Confirmed working with RS232/PPI cable and S7-200 |
| WinCC Flexible Runtime | 2007 | Same configuration procedure; verify hotfix level if issues persist |
| STEP 7 Micro/WIN | V4.0 SP6 and later | Required to set the S7-200 PPI port address and baud rate |
| S7-200 CPU | CPU 22x family | Port 0/Port 1 PPI mode supported on all standard CPUs |
| TP177B panel | 6" mono or color | Acts as a second PPI master; do not co-master with PC unless addressed correctly |
Cable Selection: USB/PPI vs. RS232/PPI
Both cables ship from Siemens as Multi-Master devices, meaning they can share the PPI bus with another master (for example, a TP177B and a PC at the same time). Only the RS232 variant, however, exposes a standard COM port to the WinCC Flexible Runtime channel DLLs and the Set PG/PC Interface applet.
| Parameter | RS232/PPI Multi-Master (6ES7 901-3CB30-0XA0) |
USB/PPI Multi-Master (6ES7 901-3DB30-0XA0) |
|---|---|---|
| PC side connector | DB-9 male (RS232) | USB Type-A |
| S7-200 side | RS485 PPI (DB-9 to PPI port) | RS485 PPI (DB-9 to PPI port) |
| WinCC Flexible Runtime support | Yes | No (in this configuration) |
| STEP 7 Micro/WIN support | Yes | Yes |
| Multi-master capable | Yes (DIP switch on cable) | Yes (DIP switch on cable) |
| Driver | Native Windows COM port | Siemens USB-to-virtual-COM driver required |
The root cause of the incompatibility is the way WinCC Flexible Runtime instantiates the PPI driver for the S7-200 channel. It enumerates native COM ports and binds the S7ONLINE access point to a PC/PPI interface entry that maps to a physical UART. A USB-to-virtual-COM bridge, even when enumerated as COMx, is not enumerated as a PC/PPI cable in the legacy Set PG/PC Interface list, so the channel fails to open.
Set PG/PC Interface Configuration
The PC side must be configured before WinCC Flexible Runtime can open a channel. Use the Windows Control Panel → Set PG/PC Interface applet (or the SIMATIC Manager equivalent on engineering stations that have STEP 7 installed).
- Open Control Panel → Set PG/PC Interface.
- For the Access Point of the Application dropdown, select S7ONLINE.
- In the Interface Parameter Assignment Used list, select PC/PPI Cable (PPI) bound to the COM port where the RS232/PPI cable is connected (typically
COM1). - Click Properties and configure the cable parameters:
| Property | Value | Notes |
|---|---|---|
| Transmission rate | 19.2 kbps | Must match the S7-200 PPI port baud rate |
| Transmit timeout | 30 s default | Raise to 60 s on noisy links |
| Receive timeout | 30 s default | Raise to 60 s on noisy links |
| Address on bus | 0 (PC master) | Must differ from the S7-200 CPU address |
| Highest station address | 31 | Default PPI token ring maximum |
| Network profile | PPI | Do not select DP for an S7-200 PPI port |
The 19.2 kbps setting is the most common failure point. WinCC Flexible Runtime will not renegotiate the baud rate; if the S7-200 port is at 9.6 kbps and the cable is at 19.2 kbps, the channel opens, no tags update, and the diagnostic buffer stays empty. Always re-check the baud rate on both sides after any firmware update or project transfer.
WinCC Flexible Runtime Connection Setup
Inside the WinCC Flexible project (the same project is compiled to the TP177B and to the PC Runtime), the connection is defined under Communications → Connections.
- Open the project in WinCC Flexible 2007 (or 2005 SP1 HF7).
- Navigate to Project → Communications → Connections.
- Double-click the first connection row and set:
| Field | Value |
|---|---|
| Name | Connection_1 (or descriptive label) |
| Driver | MPI/DP (not "PPI" - the S7-200 driver is exposed under MPI/DP) |
| Active | Enabled |
| CPU | S7-200 |
| Station address | 2 (default S7-200 PPI address) |
| Slot | 0 |
| Rack | 0 |
| Network profile | PPI |
| Highest station address | 31 |
| Transmission rate | 19.2 kbps |
Do not enable more than one connection row. Even an unused, disabled connection of the same type can cause the Runtime to attempt parallel token arbitration. If a second S7-200 must be addressed, route the data through the first CPU using NETR/NETW instructions, or add a second physical RS232/PPI cable on a different COM port and define a second Set PG/PC Interface entry.
S7-200 CPU Configuration
The PPI port on the S7-200 must be configured in STEP 7 Micro/WIN to match the PC side.
- Open STEP 7 Micro/WIN and connect to the S7-200 with the same RS232/PPI cable (or temporarily with the USB/PPI cable, which Micro/WIN supports).
- Open System Block → Communication Ports.
- Set Port 0 (or Port 1 if used) to:
| Parameter | Value |
|---|---|
| Address | 2 (or any unused PPI address ≠ 0) |
| Baud rate | 19.2 kbps (must match WinCC) |
| Mode | PPI master or PPI slave (slave is the safer default) |
| Highest station address | 31 |
Download the system block to the S7-200. A power cycle is normally required for the new baud rate to take effect.
TP177B Compatibility Considerations
If a TP177B panel is also connected to the S7-200 PPI port, it acts as a second master on the bus. The cable topology is a daisy chain with termination at both ends only.
- Use the RS232/PPI Multi-Master cable (6ES7 901-3CB30-0XA0) on the TP177B side if the panel is fed from its RS232 port. Newer TP177B 6" color variants expose a PPI/RS485 port and ship with a PPI cable.
- Set the TP177B PPI address to 1 and the PC master to 0, leaving the S7-200 at 2. Three stations on a PPI bus is well within the 32-station limit.
- Match the baud rate on the TP177B transfer settings (under Control Panel → Transfer on the panel) to the same 19.2 kbps used by WinCC Flexible and the S7-200 system block.
- If WinCC Flexible 2007 fails to connect to a TP177B via the RS232/PPI multimaster cable, first re-flash the panel firmware and confirm the project was compiled for the correct panel variant (TP177B 6" mono vs. color). Some 2007 hotfixes regressed PPI transfer on early TP177B hardware.
Baud Rate and Token-Ring Timing
PPI is a token-passing protocol on RS485. At 19.2 kbps the worst-case token rotation time with three masters is typically under 200 ms, which is well within the WinCC Flexible acquisition cycle (250 ms default). If you raise the baud rate to 187.5 kbps, the rotation drops to under 25 ms, but you must confirm the S7-200 CPU supports it - CPU 224 and higher do; CPU 221/222 are limited to 38.4 kbps on Port 0.
| Baud rate | Token rotation (3 masters, 32 stations) | S7-200 support |
|---|---|---|
| 9.6 kbps | ~400 ms | All CPUs |
| 19.2 kbps | ~200 ms | All CPUs (recommended) |
| 38.4 kbps | ~100 ms | CPU 222 and higher |
| 187.5 kbps | ~25 ms | CPU 224 and higher |
Troubleshooting Matrix
| Symptom | Likely cause | Corrective action |
|---|---|---|
| Runtime starts, no tags update, no error in channel log | Baud rate mismatch between PC and S7-200 | Set both sides to 19.2 kbps; cycle power on S7-200 |
| Runtime reports "Cannot connect to station" | Wrong cable (USB/PPI) | Replace with RS232/PPI Multi-Master (6ES7 901-3CB30-0XA0) |
| Connection drops every 2-3 minutes | Token-ring starvation from multiple WinCC connections | Reduce to one WinCC connection per S7-200 |
| PC shows COM port in Device Manager but Set PG/PC Interface does not list it | USB-to-serial bridge enumerating as COMx | Install native RS232 (PCI/PCIe) card or use a PC with built-in COM |
| TP177B transfers project, but Runtime cannot read tags | TP177B and PC both configured as master with same address | Reassign: TP177B=1, PC=0, S7-200=2 |
| Intermittent timeouts on long cable runs | Missing or incorrect termination on RS485 | Enable termination DIP switch on PPI cable, max bus length 1200 m at 9.6 kbps |
| WinCC Flexible 2007 cannot load connection to TP177B | Hotfix regression on TP177B PPI transfer | Apply latest WinCC Flexible 2007 hotfix; reflash TP177B firmware |
Verification Procedure
- Power-cycle the S7-200 after downloading the system block.
- Open Set PG/PC Interface and click Diagnostics on the PC/PPI entry. Confirm the cable is reachable (the applet reports "OK").
- Start WinCC Flexible Runtime. Open the Tools → Connection Status dialog (or the equivalent in 2005) and confirm
Connection_1is Connected. - Add a single tag of type
Wordat addressVW0and tie it to an I/O field. Type a value, click Write, and read it back from STEP 7 Micro/WIN to confirm the round trip. - If a TP177B is present, perform the same round-trip from the panel and confirm the value updates on both the panel and the PC Runtime within one acquisition cycle.
Field-Proven Cautions
- Never hot-plug the RS232/PPI cable while the S7-200 is in RUN. The PPI transceiver can latch the port into a fault state that requires a power cycle to clear.
- Do not chain more than one RS232/PPI Multi-Master cable on the same PPI segment. Each cable presents a master; multiple masters at the same address produce bus collisions invisible to the WinCC channel log.
- When upgrading from WinCC Flexible 2005 to 2007, recompile the project and re-download the system block to the S7-200. The 2007 channel DLLs renegotiate the PPI token and a stale system block can produce a one-shot timeout on first connect.
- If the S7-200 CPU is a 224XP or 226 with two ports, use Port 1 for the PC link and Port 0 for the TP177B. This isolates the HMI traffic from the Runtime traffic and prevents token-ring contention during large tag polls.
Related Documentation
- Siemens Support: S7-200 PPI communication basics
- Siemens Support: WinCC Flexible Runtime connection to S7-200
- Siemens Support: RS232/PPI Multi-Master cable (6ES7 901-3CB30-0XA0) manual
FAQ
Does WinCC Flexible Runtime support the USB/PPI Multi-Master cable (6ES7 901-3DB30-0XA0) with an S7-200?
No. The USB/PPI Multi-Master cable is not enumerated as a PC/PPI interface in the Set PG/PC Interface applet and the WinCC Flexible channel DLL cannot bind to it. Use the RS232/PPI Multi-Master cable (6ES7 901-3CB30-0XA0) on a native COM port instead.
What baud rate should I use between WinCC Flexible Runtime and an S7-200 over PPI?
Set the PC, the S7-200 system block, and any TP177B on the bus to 19.2 kbps. This is the most common production setting, supported by every S7-200 CPU, and gives a token rotation of roughly 200 ms with three masters.
Can I run more than one WinCC Flexible connection to the same S7-200 over a single RS232/PPI cable?
No. Configure a single MPI/DP connection per S7-200 in the WinCC Flexible project. Multiple connections to the same CPU over one cable starve the PPI token ring and cause intermittent timeouts that look like cable faults.
Why does my TP177B work for project transfer but WinCC Flexible Runtime still cannot read tags?
Most likely the PC master and the TP177B master are configured with the same PPI address, or the baud rates differ. Assign TP177B=1, PC=0, S7-200=2 and set all three devices to 19.2 kbps.
Does the procedure differ between WinCC Flexible 2005 SP1 HF7 and WinCC Flexible 2007?
No. The PG/PC interface entry, the single MPI/DP connection, and the 19.2 kbps baud rate are identical. If WinCC Flexible 2007 cannot connect to a TP177B, apply the latest hotfix and reflash the panel firmware before changing the wiring.