Integrating ET200B Remote I/O with S7-1500 CPU 1515-2 PN via PROFIBUS DP

The Siemens ET200B distributed I/O family (discontinued in 2015) remains widely deployed in brownfield installations. Many automation engineers face the challenge of integrating these legacy S7-1500 CPU 1515-2 PN controllers paired with either the CM 1542-5 or CP 1542-5 PROFIBUS module. This technical reference documents a validated integration path, the differences between the two PROFIBUS modules, GSD handling, baud-rate behavior, and field-proven commissioning steps.

1. System Architecture Overview

The integration architecture consists of three logical layers:

• Controller layer: SIMATIC S7-1500 CPU 1515-2 PN with integrated PROFINET interfaces.
• PROFIBUS master layer: External CM or CP PROFIBUS module plugged into the S7-1500 backplane.
• Legacy I/O layer: ET200B remote I/O stations connected as PROFIBUS DP slaves.

The CPU communicates with the PROFIBUS master module over the S7-1500 backplane (internal S7-1500 system bus). The CM/CP then operates as a Class 1 PROFIBUS DP master on the field-level RS-485 segment. This dual-stack approach lets an engineer keep a PROFINET-only CPU while still accessing legacy PROFIBUS devices through a single TIA Portal project.

2. Hardware Components and Order Numbers

2.1 S7-1500 CPU

Refer to the official CPU 1515-2 PN (6ES7515-2AN03-0AB0) technical documentation for the full performance specification, including bit-instruction execution times, work-memory sizes, and supported module counts.

2.2 PROFIBUS Master Module Selection

Recommendation for this task: Both modules work as a DP master. The CP 1542-5 is the preferred choice when the network must also carry S7 routing, PG diagnostics, or when the PROFIBUS master should offload communication from the CPU. The CM 1542-5 is sufficient and more cost-effective for plain DP master operation against ET200B slaves.

2.3 ET200B Module Inventory

The ET200B family uses the terminal-block concept where each block carries screw or spring terminals and accepts one or two electronic sub-modules.

3. Prerequisites

1. TIA Portal/STEP 7 Professional V15 or newer (V16, V17, V18 also validated for ET200B GSD import; older TIA versions may refuse older GSD revisions).
2. Original ET200B GSD files (Siemens GSD for the ET200B series dates from approximately 2000). Store them in a known directory (e.g., C:\Siemens\GSD\ET200B) before launching TIA Portal.
3. GSD-import-compatible hardware catalog: confirm the option Options > Manage General Station Description Files (GSD) is available in the TIA Portal installation.
4. Firmware consistency: the GSD revision must match the firmware on the physical ET200B station. Mismatches typically do not break DP-V0 operation but can lock out DP-V1 diagnostics.
5. PROFIBUS cable (purple, twisted pair with shield) and PROFIBUS connectors with terminating resistor enabled at both line ends.
6. 24 V DC load supply for the DO modules with sufficient current headroom for the connected actuators.

4. Step-by-Step Integration Procedure

Step 1 — Install the ET200B GSD

1. Open TIA Portal and the target project.
2. Navigate to Options > Manage General Station Description Files (GSD).
3. Browse to the directory containing the ET200B .gsd files.
4. Select each file, then click Install. TIA Portal places the devices in the hardware catalog under Other field devices > PROFIBUS DP > ET200B.

Step 2 — Add the CPU and PROFIBUS Master Module

1. Insert the CPU 1515-2 PN (6ES7515-2AM01-0AB0 or 6ES7515-2AN03-0AB0) into the S7-1500 station.
2. Drag the CM 1542-5 or CP 1542-5 into an empty slot of the same S7-1500 station. The slot assignment appears in the device view.
3. Open the CM/CP properties, select PROFIBUS interface > [Add new subnet], and configure the desired baud rate.

Step 3 — Configure the DP Master

1. Assign the DP master role in the CM/CP properties (operator control: Operating mode = DP master).
2. Set the bus parameters: baud rate, highest station address (HSA), and Ttr (target rotation time). Defaults from Siemens for 1.5 Mbps are HSA = 126 and Ttr = 30000 bit-times.
3. Confirm the slot-time, min-station-delay, and quiet-time are auto-calculated for the chosen baud rate.

Step 4 — Insert ET200B Stations as DP Slaves

1. In the network view, drag each ET200B variant from the hardware catalog onto the PROFIBUS subnet.
2. Assign a unique PROFIBUS address to each station (range 1-125; addresses 0, 1, and 126 are reserved).
3. Open each ET200B slave and assign the correct terminal block (6ES7193-0CB10-0XA0) and slot population (16 DI, 16 DO, 32 DI, 32 DO).

Step 5 — Compile and Download

1. Right-click the S7-1500 station and select Compile > Hardware (rebuild all).
2. Verify that no compilation errors are reported in the Inspector window.
3. Download the hardware configuration to the CPU (online > accessible devices > download to device).

5. PROFIBUS Baud Rate Behavior

PROFIBUS DP supports standardized baud rates from 9.6 kbps to 12 Mbps. The ET200B stations tested in the source validation successfully operated at three intermediate rates:

At 1.5 Mbps, maximum segment length is 200 m without repeaters; above 1.5 Mbps (e.g., 3, 6, 12 Mbps), ET200B hardware is also capable but the cable length drops sharply. For most ET200B retrofits inside existing cabinets, 1.5 Mbps is the recommended default and matches what was successfully tested.

6. Diagnostics and Status Indicators

The ET200B stations report DP-V0 diagnostic frames. Each module has front-panel SF (system fault) and BF (bus fault) LEDs. The CM/CP 1542-5 reports the same LEDs plus a MAINT indicator for maintenance events.

7. Module-Slot Configuration Example

For a 16 DI + 16 DO combination on a single terminal block (6ES7193-0CB10-0XA0), the slot mapping is:

Address ranges can be reassigned in the device view of TIA Portal. For 32-channel modules, allocate 4 bytes per slot.

8. Troubleshooting Matrix

9. Verification Procedure

1. Online diagnostics: Right-click the CM/CP and select Online & diagnostics. Confirm "DP master OK" status.
2. Slave list: Open DP master system > slave list. All ET200B slaves must appear with status "Data Exchange."
3. I/O test: Use a watch table in TIA Portal to force and read each input/output byte. Confirm physical behavior on the field terminals.
4. Cyclic logging: Enable the diagnostic buffer on the CM/CP. Check for bus errors, retries, or diagnostic frames.
5. Long-run test: Run for 24 hours at the chosen baud rate to catch intermittent issues.

10. Firmware and Lifecycle Considerations

The ET200B family entered phase-out / discontinuation in 2015. Spare-part availability is now handled through the Siemens Classic Automation program. The following points apply:

• Firmware updates: No further firmware updates are issued for ET200B modules. The last released firmware remains the operational baseline.
• CM 1542-5 / CP 1542-5 firmware: Siemens periodically releases firmware updates for the PROFIBUS master modules. Confirm the firmware revision is compatible with the TIA Portal version used (cross-reference in the TIA Portal "Compatibility tool").
• CPU 1515-2 PN firmware: Always update the CPU firmware to the latest release before commissioning to ensure stable CM/CP communication.
• Migration path: When an upgrade is feasible, replace ET200B with ET200SP or ET200MP modules. The PROFIBUS DP cable plant can be retained with a PROFIBUS-to-PROFINET gateway (e.g., IE/PB Link PN IO) if the master side is migrated first.

11. Field-Proven Practical Notes

From the validation report that prompted this article, several practical observations can be made:

• The integration of ET200B stations with the S7-1500 / CP 1542-5 combination functioned without any unusual configuration steps beyond importing the legacy GSD file.
• Other legacy PROFIBUS devices (third-party CNC controllers, robots, tomographs) have been successfully connected to the same architecture. The main verification step is to confirm GSD/firmware consistency.
• GSD-version mismatches between the device firmware and the TIA Portal acceptance range are rare in practice but can be diagnosed by attempting to compile the configuration: a successful compile is the strongest signal of compatibility.
• Always keep a copy of the original Siemens-issued GSD file alongside the project archive.

12. Quick Decision Matrix: CM 1542-5 vs CP 1542-5