Configuring Siemens Coros OP25: ProTool Setup & S7-200 PPI Wiring Reference

The Siemens Coros OP25 (MLFB 6AV3525-1EA01-0AX0) is a text-and-graphic operator panel from the OP25/OP35/OP45 family that Siemens AG discontinued in 1999. Despite its end-of-life status, large numbers of OP25 units remain installed in legacy machines, training labs, and retrofit spare-part inventories. Because the panel was engineered against the same ProTool/ProTool/Lite configuration runtime that drives later OP27, OP37, OP170, and TP170A panels, an OP25 is a useful low-cost platform for learning Siemens HMI commissioning before moving to TIA Portal / WinCC Flexible Compact.

This reference consolidates the official Siemens Support entry (entry ID 1142693) for the OP25/OP35/OP45 family, the practical wiring requirements for connecting an OP25 to an S7-200 CPU 222 over PPI, and the PC-side programming cable used to load ProTool projects. The article is written for an engineer or technician who has just acquired a surplus OP25, has an S7-200 in hand, and needs to bring the panel online without resorting to legacy forum posts.

1. OP25 Product Family Overview

The OP25, OP35, and OP45 belong to the first generation of Siemens Coros text/graphical operator panels designed to sit alongside the SIMATIC S5, S7-200, and S7-300 controllers of the mid-1990s. All three share the same ProTool project environment and the same physical RS-485 PPI/MPI backplane, but differ in display size, function-key count, and supply voltage option.

Cross-reference: Siemens Support entry 1142693 - Operator Panel OP25, OP35, OP45.

2. MLFB Breakdown of 6AV3525-1EA01-0AX0

Siemens MLFB (Machine-Readable Product Designation) decoding is essential when ordering spares, sourcing replacement firmware EPROMs, or matching an OP25 to its sibling variants. The 6AV3525 family encodes the panel as a SIMATIC HMI (6AV), text/graphic class (35), 25 series, with the remaining positions specifying the display variant and options.

If the suffix differs (for example -0BX0 for backlit variants or an AC supply version), consult the device rating plate before applying any wiring diagram in this article. Mismatched supply voltages between DC and AC variants are the single most common failure on OP25 units pulled from surplus.

3. ProTool Software Environment

The OP25 is configured exclusively with the ProTool package (or the slimmed-down ProTool/Lite for text-only panels). ProTool is a 16-bit Windows 3.11/95/98 era IDE that later evolved into ProTool/Pro and ultimately into WinCC Flexible and TIA Portal's WinCC. The OP25 firmware does not accept projects generated by WinCC Flexible, so a working ProTool installation is mandatory for first-time commissioning.

3.1 Required software stack

• ProTool V6.0 SP3 or later (the last release that targets OP25/OP35/OP45). Earlier service packs are usable but lack bug fixes for OP25 EPROM transfer.
• ProTool/Lite V6.0 for text-only projects on the OP25.
• Windows 9x / Windows NT 4.0 / Windows 2000 as the host operating system. ProTool was not compiled for Windows XP or later; if you must run it on a modern PC, use a Windows XP Mode virtual machine or a DOSBox/PCem legacy environment with a real serial port passed through.
• GSD file for the OP25 if you intend to integrate it as a Profibus-DP slave (download from Siemens Support, see Section 8).

3.2 Creating a new OP25 project

1. Launch ProTool and choose File > New.
2. In the device-selection dialog, set the family to OP25 and confirm the OP25 variant (text, 2 x 20).
3. Select the controller protocol. For an S7-200 CPU 222, choose SIMATIC S7-200 PPI. For an S7-300/400, choose SIMATIC S7 MPI or Profibus-DP.
4. Define the station address. PPI defaults: panel address 1, PLC address 2. The bus must be terminated at both ends.
5. Create screens, assign tags to PLC addresses (for example VW0, VW100, MB10), and configure alarms.
6. Compile the project (F7) and transfer it to the OP25 (Section 4).

4. PC-to-OP25 Programming Cable (Serial)

Unlike modern Siemens panels that accept Ethernet, the OP25 only exposes an RS-232 service port on its underside. This port is used for both project download and firmware upload, and it uses a Siemens proprietary pin-out that does not match a stock DB9 null-modem cable.

4.1 OP25 RS-232 service port pinout

4.2 PC-side cable construction

Build a shielded serial cable with the following minimum wiring:

• PC DB9 pin 2 (TXD) -> OP25 pin 3 (RXD)
• PC DB9 pin 3 (RXD) -> OP25 pin 2 (TXD)
• PC DB9 pin 5 (GND) -> OP25 pin 5 (GND)
• Shield connected only at the PC chassis, floated at the OP25 end to avoid ground loops.
• Loop back PC-side pins 4-6 and 7-8 only if your PC terminal-emulation software requires DSR/CTS handshake. The OP25 does not implement hardware flow control on the service port.

4.3 Transfer procedure

1. Connect the cable between the PC COM port and the OP25 service port while power is off.
2. Power on the OP25 and enter Transfer mode by holding the ESC + F1 keys during the boot self-test until the panel prompts Transfer mode active.
3. In ProTool, choose File > Transfer > to Panel. Select the correct COM port (typically COM1) and baud rate (default 9600, switchable to 19200 in the OP25 setup menu).
4. Click Start. Transfer time for a 64 KB OP25 project is typically 30-90 seconds at 19200 baud.
5. The OP25 reboots automatically and runs the new project.

5. PPI Wiring to S7-200 CPU 222

The OP25 communicates with an S7-200 CPU 222 over the Siemens PPI (Point-to-Point Interface) protocol, which is a proprietary RS-485 master/slave bus running at 9600 or 19200 baud. The OP25 acts as a PPI master and the CPU 222 as a slave at address 2 by default.

5.1 S7-200 Port 0 / Port 1 RS-485 pinout

5.2 OP25 PPI/MPI port pinout

The OP25 PPI/MPI port is a DB9 female on the panel underside. The relevant signals are pins 3, 5, and 8; pin 1 is shield; pins 4 and 9 are sometimes used for bus termination switching in DP variants.

5.3 Straight PPI cable between OP25 and CPU 222

For an OP25 connected directly to a single CPU 222, a point-to-point PPI cable is the simplest valid topology:

• OP25 pin 3 -> CPU 222 pin 3 (Data B)
• OP25 pin 8 -> CPU 222 pin 8 (Data A)
• OP25 pin 5 -> CPU 222 pin 5 (Signal ground)
• Shield bonded at one end only - typically at the PLC cabinet ground bar.

This answers the recurring question: "Is the PPI cable between PLC and OP25 just pins 3 and 8 on both devices (+shield)?" - Yes. Pins 3 and 8 carry the differential RS-485 pair, pin 5 (or pin 1 shield) is the reference, and no other signals are required for a single-master / single-slave configuration.

5.4 Multi-drop PPI bus (OP25 plus STEP 7-Micro/WIN)

If the same CPU 222 must also be reached by STEP 7-Micro/WIN on a PC (for program upload/download), the OP25, the PC/PPI cable, and the CPU 222 are placed on a single RS-485 segment. In that case the bus must be terminated at both physical ends with 120 ohms between pins 3 and 8.

For multi-drop, the OP25 is configured as PPI master with address 1, the CPU 222 as PPI slave with address 2, and the STEP 7-Micro/WIN PC/PPI cable as a second PPI master. STEP 7-Micro/WIN should set its PPI master address to 0 (the default) and only run transfers when the OP25 is not actively polling.

6. Profibus-DP Integration (Optional)

Although PPI is the most straightforward path to an S7-200, the OP25 also supports Profibus-DP slave operation in the -1EA variant. The official Siemens GSD file lists the panel as a compact DP slave with input and output word areas.

6.1 GSD file acquisition

The GSD file for the OP25 is distributed through the Siemens Support entry 1142693. Download SIEM802D.GSD (or the equivalent family GSD) and import it into the Profibus master configuration (STEP 7 HW Config, COM Profibus, or a third-party Profibus configurator). When importing, set the OP25 station address to a unique value on the segment (3 is a common choice to keep 1 and 2 reserved for any PC/master).

6.2 I/O slot mapping

7. Power, Grounding, and Mechanical Installation

7.1 Supply wiring

• 24 V DC nominal (DC variants), 20.4 V to 28.8 V tolerance, including ripple.
• Typical inrush 1.5 A for 50 ms at cold start (LCD backlight surge).
• Use a regulated PELV/SELV supply, fused at 2 A slow-blow.
• For AC variants (OP45 only) connect L/N/PE per the rating plate and verify that the variant you received is in fact AC-rated before applying power.

7.2 Panel cutout and torque

• Cutout: 138 mm x 68 mm (plus 1 mm tolerance per side).
• Mounting clamp torque: 0.4 N m. Over-tightening cracks the bezel, a very common failure on legacy OP25 units.
• IP65 on the front face when correctly clamped with the supplied gasket.

8. Step-by-Step Commissioning Procedure

1. Inspect the OP25 for physical damage to the LCD, keypad, and rear connector. Verify the rating plate MLFB matches the project target.
2. Apply 24 V DC and confirm the OP25 performs its self-test (all LCD segments on, then firmware version banner).
3. Enter the OP25 setup menu (hold F1 + F8 during power-up) and record the firmware version, transfer baud rate, and PPI address.
4. Connect the RS-232 programming cable (Section 4) and transfer the compiled ProTool project.
5. Disconnect RS-232 and connect the PPI cable to the CPU 222 (Section 5).
6. Power-cycle the CPU 222 with the OP25 already powered; the OP25 establishes a PPI master/slave session and shows the first configured screen.
7. Toggle a digital output in the PLC to confirm tag updates flow back to the OP25 in under 1 second.
8. Trigger each configured alarm and verify the OP25 logs it correctly to the alarm buffer.
9. Archive the ProTool *.pdb file, the transfer log, and a screenshot of the OP25 running screen as commissioning evidence.

9. Verification Checklist

10. Troubleshooting Matrix

11. Migration Path: OP25 to OP27 or Modern Panels

The OP27 is the direct, drop-in successor of the OP25. The cutout, PPI/MPI port pinout, and ProTool project file are compatible. The Siemens SiePortal migration thread confirms that the original OP25 *.pdb project must be retained for the migration, because ProTool cannot reverse-engineer a project from the panel's runtime image.

For new installations, skip the OP25 entirely and design directly against a TP177, KP400 Comfort, or KTP400 Basic using TIA Portal / WinCC. The OP25 is appropriate only for:

• Repair of identical existing units where downtime is the priority.
• Training labs that need a low-cost Siemens PPI master.
• Spare-parts cannibalization where donor OP25 electronics are harvested for an OP27 that lacks a working backlight.

12. Spares and Documentation Sources

• Siemens Support entry 1142693 - Operator Panel OP25, OP35, OP45 (English)
• Siemens Support entry 1142693 - Operator Panel OP25, OP35, OP45 (worldwide locale)
• Siemens SiePortal - changing from the Coros OP25 to OP27