ABB PM856K01 3BSE018104R1 Retrofit-Ready CPU for AC 800M Control Systems
The ABB PM856K01 (order number 3BSE018104R1) is a high-performance central processing unit designed for the AC 800M Distributed Control System platform — one of ABB’s most widely deployed process automation architectures in the power, oil & gas, pulp & paper, and chemical industries. As legacy AC 800M installations approach end-of-life or face discontinued spare parts availability, the PM856K01 has become the preferred retrofit-ready replacement for earlier CPU variants including the PM851, PM860, and PM861 modules. Its backward-compatible backplane interface and support for the MMS/IEC 61850 communication stack make it a technically sound choice for both like-for-like swaps and full control system modernization projects.
Upgrade Compatibility Table
| Parameter | PM856K01 3BSE018104R1 | Notes / Retrofit Guidance |
|---|---|---|
| Platform | ABB AC 800M | Compatible with S800 I/O and CI modules |
| Replaces | PM851, PM860, PM861 | Direct backplane replacement; verify firmware revision |
| Backplane Interface | AC 800M standard rack | No mechanical adapter required for same-generation racks |
| Communication Ports | 2× Ethernet (10/100), RS-232 | Supports Profibus DP via CI840A; FOUNDATION Fieldbus via CI873 |
| Communication Protocols | MMS, IEC 61850, Modbus TCP, OPC | Verify CI module compatibility for legacy Profibus links |
| Memory | 32 MB RAM / 8 MB Flash | Sufficient for large application programs; check project size |
| Power Supply Compatibility | 24 VDC via rack (SS822, SS823) | Confirm power budget with I/O load before installation |
| Programming Tool | ABB Control Builder M | Application backup required before CPU swap |
| Installation | Hot-swap capable (with precautions) | Recommended: cold swap with full program restore |
| Warranty | 12-Month Warranty | Covers hardware defects; includes pre-shipment functional test |
Retrofit Planning for Existing Automation Systems
Successful integration of the PM856K01 into an existing AC 800M control cabinet begins well before the physical swap. Engineers should start by auditing the current rack configuration — typically an TP830 or TB840 rack — to confirm available slot positions and total power draw. The PM856K01 draws approximately 4.5 W from the backplane; when combined with active S800 I/O modules such as the AI810 analog input module, AO810 analog output module, DI810 digital input module, and DO810 digital output module, the aggregate load must remain within the SS822 or SS823 power supply rating.
Communication architecture is the next critical checkpoint. Sites running legacy Profibus DP networks will need to retain or upgrade their CI840A communication interface module, which plugs into the same rack and handles the Profibus master function independently of the CPU. For sites migrating toward Ethernet-based fieldbus, the CI873 FOUNDATION Fieldbus HSE interface or CI854 Profibus DP interface can be retained alongside the new PM856K01 without any rack modification. If the plant uses a redundant CPU configuration, a second PM856K01 unit is required along with the appropriate redundancy cable — the existing TB840A redundancy module remains compatible.
Terminal wiring on the S800 I/O side does not change during a CPU swap, which significantly reduces retrofit risk. Field cables connected to the S800 I/O terminal units remain in place; only the CPU module and, if necessary, the CI communication modules are exchanged. Before removal of the old CPU, a full application backup must be exported from ABB Control Builder M, including all function block diagrams, SFC sequences, and hardware configuration files. The PM856K01 supports the same IEC 61131-3 programming environment, so existing logic can be restored directly after the new module is seated and powered.
For sites that also operate ABB Panel 800 HMI systems or third-party SCADA platforms connected via OPC DA/UA, the communication link configuration in Control Builder M must be verified post-swap to ensure the IP address assignment and OPC server tag paths remain consistent. Any change to the CPU’s Ethernet port IP address will require corresponding updates in the HMI project and historian configuration.
Downtime Control During System Migration
Minimizing unplanned downtime is the primary concern for any CPU replacement in a live production environment. The recommended approach for PM856K01 installation is a planned maintenance window with a structured cold-swap procedure. Prior to shutdown, operators should place all control loops in manual mode and confirm that field devices — including control valves, variable frequency drives, and safety interlocks — are in a safe hold state. The existing CPU’s application program, hardware configuration, and event log should be exported and stored on an offline engineering workstation.
Once the PM856K01 is seated in the rack and powered, Control Builder M is used to download the restored application. The module performs a self-test sequence lasting approximately 30–60 seconds before entering RUN mode. Engineers should verify all S800 I/O module status LEDs, confirm Profibus or Ethernet communication link status on the CI modules, and perform a point-by-point I/O check before returning loops to automatic control. For redundant CPU configurations, the standby PM856K01 should be synchronized and confirmed healthy before the primary is declared operational.
Sites with strict SIL-rated safety loops should coordinate the CPU swap with their functional safety engineer and ensure that the Safety Instrumented System — whether an ABB AC 800M HI or a separate Triconex/Yokogawa platform — remains in a defined safe state throughout the migration. The PM856K01 itself is not a SIL-rated module and must not be used as the primary safety controller in SIL 2/3 applications without appropriate architectural separation.
Retrofit Support FAQ
Q1: Is the PM856K01 3BSE018104R1 a direct drop-in replacement for the PM860K01?
A: Yes, the PM856K01 is mechanically and electrically compatible with the same AC 800M rack slots used by the PM860K01. The backplane connector pinout is identical. However, firmware versions differ, and the application program must be re-downloaded using ABB Control Builder M after installation. No wiring changes to S800 I/O terminal units are required.
Q2: What pre-shipment testing is performed on the PM856K01?
A: Each unit undergoes a functional power-on test, backplane communication verification, and Ethernet port continuity check before dispatch. Units are supplied with a 12-month warranty covering hardware defects under normal operating conditions. A test report is available upon request.
Q3: Can the PM856K01 support both Profibus DP and Modbus TCP simultaneously?
A: Yes. The PM856K01 supports multiple communication protocols concurrently through its onboard Ethernet ports (Modbus TCP, OPC, MMS) and via CI communication interface modules installed in the same rack. A CI840A handles Profibus DP mastering independently, allowing both protocols to operate in parallel without CPU performance impact.
Q4: What is the lead time and warranty coverage?
A: Units are dispatched from verified stock within 1–3 business days. A 12-month warranty is provided from the date of shipment, covering manufacturing defects and hardware failures under specified operating conditions (0–55°C, non-condensing). Warranty claims are processed via [email protected].
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