ABB PM858-C 3BSE093350R1 | AC 800M CPU Replacement

Description

Key Technical Specifications

ABB’s own AC 800M data sheet confirms the 33 MHz MPC866 processor, 16 MB RAM, 7.147 MB application RAM, flash storage, and CPU redundancy support for PM858.

One caution: some current secondary listings publish 24 VDC, operating-temperature, memory, and interface details that do not agree with ABB’s official PM858 documentation. I would not use those secondary figures for an engineering specification without checking the exact hardware revision.

PM858-C

Application Scenarios & Pain Points

A failed AC 800M CPU can take down far more than one process loop. In a plant with hundreds of S800 I/O points, the controller is the traffic center of the automation system; a questionable replacement can create a much larger commissioning problem than the original hardware failure.

Typical Applications

• Process DCS: Used as the CPU platform for AC 800M process-control applications, executing application logic and coordinating distributed I/O.
• S800 I/O Systems: The PM858 works within the AC 800M architecture that supports S800 I/O and communication modules. ABB’s documentation specifically identifies S800 I/O connectivity and CEX-bus-related accessories around the PM858 platform.
• Redundant Controller Applications: PM858 supports CPU redundancy, making it suitable for installations where loss of one processor should not immediately stop the process.
• Legacy AC 800M Maintenance: Particularly useful when an established AC 800M installation must remain operational rather than being migrated during an emergency outage.

Field Case:
On a redundant process controller, the first instinct is often to replace the processor showing the alarm. A better sequence is to check the redundancy state, controller diagnostics, CEX-bus status, communication modules, and firmware compatibility first. A dirty backplane connector or failed communication interface can make a healthy CPU look guilty.

Related Products

• — The base processor designation for the supplied -C hardware. ABB documents as an AC 800M CPU using an MPC866 processor, 33 MHz clock, and 16 MB RAM. It is the closest functional reference when verifying the supplied part.
• ABB PM858K01 — Processor Unit Kit containing one CPU and the associated required items. It is useful when the requirement is a complete processor-unit package rather than the processor module alone. ABB lists 3BSE082895R1 for this configuration.
• ABB PM858K02 — Redundant processor-unit kit containing two PM858K01 units. This is intended for redundant CPU arrangements and is materially different from purchasing one standalone . ABB lists 3BSE082896R1 for this configuration.
• ABB PM856A — Lower-performance AC 800M CPU using an MPC860 processor. It has different processing capability and does not provide the same redundancy feature, so it is not a direct substitute.
• ABB PM860A — Higher-clock AC 800M processor using an MPC860 at 48 MHz. It belongs to the same CPU family but has different hardware characteristics and application compatibility requirements.
• ABB PM861A — Classic AC 800M processor with an MPC860 and CPU redundancy support. It is a related redundant CPU option, but its architecture and memory characteristics differ from .
• ABB TP830 — AC 800M baseplate used to mechanically and electrically mount the processor and associated modules. It is supporting hardware, not an alternative CPU. ABB lists TP830 among the system accessories.
• ABB BC810K02 — CEX-bus interconnection unit used in AC 800M architectures. It becomes relevant where the controller configuration uses CEX-bus expansion or redundancy arrangements.
• ABB SD831 / SD832 / SD833 / SD853 / SD854 — AC 800M system power-supply options listed by ABB as associated hardware. Selection depends on the complete controller and cabinet power architecture.