WinCC to TI545 and S7-200 PLC Communication via RS-232

WinCC remains one of the most widely deployed SCADA/HMI platforms in industrial automation, and field engineers continue to face the challenge of integrating older controllers such as the Texas Instruments TI545 (Simatic TI 505 series) and the SIMATIC S7-200 CPU 22x family. Because most of these legacy devices communicate through a serial RS-232 port, the wiring, handshake configuration, and WinCC channel selection must be performed precisely to obtain a stable online connection. This reference consolidates the wiring tables, protocol parameters, channel configuration, and verification steps required to bring a TI545 or S7-200 online with WinCC V5/V6/V7 and WinCC Professional (TIA Portal).

1. Communication Architecture Overview

WinCC connects to PLCs through channels. Each channel is a software driver that translates between the WinCC tag database and a physical or logical communications path. For serial devices, the principal channels are:

For a TI545 attached to a PC, the practical approach is one of:

1. Use the SIMATIC S5 Serial 3964R channel with the TI545 in 3964R mode.
2. Use a third-party OPC server (e.g. KEPware, Matrikon) that exposes TI545 native protocol, then connect WinCC as an OPC DA client.
3. Use the Modbus Serial channel if the TI545 firmware supports Modbus RTU slave mode (TI545 firmware versions 5.x and later generally support this through a custom or third-party Modbus personality module).

For a S7-200 CPU 22x, the options are:

1. PPI (Point-to-Point Interface) over RS-485 via the PC/PPI cable (USB or RS-232 variant).
2. MPI over RS-485 through the CP5611 / CP5613 / CP5512 PC card.
3. Ethernet via the CP243-1 IT module (ISO-on-TCP).

2. RS-232 Electrical and Mechanical Reference

RS-232 (EIA-TIA-232-F) defines a single-ended voltage interface with the following electrical characteristics that are relevant when wiring industrial PLC ports:

The standard PC DE-9 pinout (TIA-574) is:

3. Null-Modem Cable for PC-to-PLC RS-232

A null-modem (crossover) cable ties the DTE outputs of the PC to the DTE inputs of the PLC. The TI545 programming port is implemented as a DTE device; the S5-100U / TI545 series expects to see its TXD driven by the PC's RXD, and vice versa. The minimum viable null-modem swaps TD/RD, RTS/CTS, and DTR/DSR, with the signal ground straight through.

3.1 Standard Null-Modem with Full Handshake (DB-9 to DB-9)

3.2 Minimal 3-Wire Null-Modem (No Handshake)

When the PLC and WinCC channel are both configured for "no flow control," only TD, RD, and GND are required. Pins 4-6-7-8 are left disconnected on each end.

4. TI545 PLC Serial Port Configuration

The TI545 (also referred to as the Simatic TI545 after Siemens acquired the TI industrial automation division) is a member of the TI505 family. Its front-panel COMM 0 port is an RS-232 port that can be configured for several protocols depending on the personality loaded in the PLC:

The serial parameters on the TI545 are set either through TISOFT (offline configuration) or via DIP switches on the CPU faceplate. Default TI545 COMM 0 settings are typically 9600 baud, 8 data bits, no parity, 1 stop bit (8N1), RTS/CTS hardware handshake enabled.

4.1 TISOFT Configuration Steps for RS-232 / 3964R

1. Connect PC COM1 to the TI545 COMM 0 port using the null-modem cable from Section 3.1.
2. Launch TISOFT and select Online > Set Up Communications.
3. Set Port = COM1, Baud = 9600, Parity = None, Data Bits = 8, Stop Bits = 1.
4. Set Protocol = TI (NITP) over 3964R or PPP depending on the loaded personality.
5. Click Connect. TISOFT should report a successful connection within 2-3 seconds.

5. WinCC Channel Configuration for TI545 via S5 Serial 3964R

WinCC V6 / V7 includes the SIMATIC S5 Serial 3964R channel. The driver implements the 3964R procedure with RK512 framing on top, which is the same procedure that TISOFT uses for online communication with the TI545.

5.1 Add the Channel in WinCC Explorer

1. Open the WinCC Explorer and right-click Tag Management.
2. Select Add New Driver → SIMATIC S5 Serial 3964R.
3. A new logical connection slot appears. Open its Connection Properties.

5.2 Connection Parameters

WinCC tags are then created using the S5 Datentyp addressing scheme. TI505 memory areas map to S5 DB/DX/W/F areas as follows:

6. WinCC Channel Configuration for TI545 via OPC Server

When the S5 Serial channel produces unstable results on heavily loaded networks, or when the controller is a non-Siemens variant, the cleanest path is an OPC Data Access server. KEPware's TI505 Serial driver (now part of KEPServerEX) implements the native TI505 protocol and exposes it to WinCC as OPC DA tags.

6.1 Configure the OPC Channel in WinCC

1. Right-click Tag Management → Add New Driver → OPC.
2. Open the OPC Groups properties and click Browse Server.
3. Select the KEPware OPC server, for example KEPware.KEPServerEX.V6.
4. Add the desired tag names with full OPC item paths such as Channel1.TI545.V1.

OPC DA works over DCOM, so Windows firewall rules on Windows 7 and later must allow opcenum, opccommand, and the OPC server executable. The Siemens knowledge base entry SIEMENS WinCC Communication Manual documents the COM/DCOM security model in detail.

7. S7-200 CPU 22x Connection to WinCC V5/V6

The S7-200 family does not support MPI master mode out of the box, and it does not appear in the WinCC S7 Protocol Suite as a selectable node. The supported integrations are:

7.1 S7-200 PC Access OPC Configuration

1. Install S7-200 PC Access V1.0 (or the SP4 / SP6 update) on the WinCC station.
2. Create a new Project, add the CPU 22x node, and configure the PPI address (default 2) and baud (9.6 kbit/s or 19.2 kbit/s).
3. Insert Items in PC Access mapping to V-memory, Inputs, Outputs, Merkers (M), or Counters/Timers as required.
4. Right-click the item → Test to verify the value is read before exposing it to WinCC.
5. Start the OPC server. The ProgID is S7200PCAccess.OPCServer.

Add the OPC channel in WinCC (as described in Section 6.1) and add the PC Access items as OPC tags. WinCC will poll them at the configured acquisition cycle (default 1 s).

7.2 S7-200 PC/PPI Cable Wiring Reference

The Siemens PC/PPI cable (order number 6ES7 901-3CB30-0XA0 for USB, 6ES7 901-3BF20-0XA0 for RS-232) is internally an RS-232-to-RS-485 converter. No custom wiring is required at the PLC end; the cable plugs into the S7-200 Port 0 or Port 1 (RS-485, 9-pin sub-D female). The drivers must be installed on the PC; without the USB-to-serial driver the COM port will not enumerate.

8. COM Port Parameter Matrix (Universal)

The following table summarizes the most common parameter sets encountered in the field. Confirm the PLC's actual configuration with a serial analyzer (e.g. Eltima Advanced Serial Port Monitor) if mismatches are suspected.

9. WinCC Runtime Verification Procedure

1. Open WinCC Explorer and start Runtime (or the configured WinCC project).
2. Watch the channel diagnosis window. The S5 Serial 3964R channel displays status OK and a green check when the connection is established.
3. Create a temporary I/O field on a screen bound to a known TI545 tag (e.g. TI545_1 / V1). The field should display the actual value of the variable, updating at the configured acquisition cycle.
4. Force a value write from WinCC: enter a value in the I/O field and press Enter. The WinCC Tag Logging or Channel Diagnosis window should show the write event and the PLC's new state.
5. Disconnect the cable and confirm WinCC raises the diagnostic alarm Connection broken within the configured timeout (default 5 s).

10. Troubleshooting Matrix

11. Cable Length and Baud Rate Derating

RS-232 cable capacitance is the dominant factor limiting distance. The rule of thumb is:

Max cable length (m) ≈ 30 / (baud rate in kbit/s) × 0.3 (capacitance factor)

At 9600 bit/s this yields approximately 30 m with low-capacitance cable (≤ 50 pF/m). At 115200 bit/s the practical limit is closer to 3 m. For runs over 15 m, convert to RS-422/485 with a converter (e.g. ICL232-based, or industrial-grade Westermo or Moxa TCC-100/120) and run differential signaling.

12. Field Commissioning Checklist

• Physical: DB-9 shells crimped, no bent pins, strain reliefs installed.
• Electrical: Shield grounded at one end only (typically the PC side); ground loop avoided.
• PLC: CPU in RUN, no active faults, COMM 0 enabled, station address known.
• WinCC: Channel driver added, logical connection configured, COM port correct, baud/parity/handshake match PLC.
• Tags: One read-only tag and one writable tag tested with known values.
• Diagnostics: Channel Diagnosis window shows green; alarm logging configured for Connection broken.

13. Document References

• WinCC Communication Manual (PDF) — Official Siemens document for WinCC V5 channel setup.
• Siemens Support Forum: PLC & WinCC connection in TIA Portal Network View — TIA Portal WinCC connection troubleshooting.
• Siemens Industry Online Support — Search for "S7-200 PC Access" and "TI505 OPC" for firmware notes and OPC server downloads.