The PM866 is a high-performance Processor Unit within ABB's AC 800M controller hardware platform, belonging to the PM8xx/TP830 series. AC 800M is a modular hardware platform comprising individual hardware units that can be configured and programmed to perform multiple control functions. As the core processing unit of this platform, the PM866 is capable of driving complex automation control applications, ranging from small programmable logic controllers to advanced distributed control systems and even high-integrity safety systems.
The PM866 must be used in conjunction with the TP830 Baseplate to form a complete processor module. This combination provides powerful processing capabilities, rich communication interfaces, and high-reliability design, making it suitable for industrial environments with high demands for control performance and system availability.
2. Hardware Composition and Physical Structure
Physically, the PM866 Processor Unit consists of two basic parts:
The Processor Unit itself: Contains the CPU board and the Power Supply board.
CPU Board: Integrates the MPC866 microprocessor (running at 133 MHz), 64 MB of SDRAM, controllers for all built-in communication interfaces, a real-time clock, LED status indicators, an INIT pushbutton, and a Compact Flash card interface.
Power Supply Board: Generates isolated, circuit-protected +5 V and +3.3 V supplies for the main board and I/O units. It also contains opto-isolated RS-232C drivers/receivers for the service port and a backup battery holder for memory/real-time clock backup.
The TP830 Baseplate: Houses the Termination Board.
The majority of external connections terminate on this board. It is grounded to the DIN-rail through the metallic components of the housing.
The termination board is provided with screw terminals for power supply and redundant power supply monitoring, RJ45 connectors for the control network and serial ports, a service port connector, and connectors for the Electrical ModuleBus and CEX-Bus.
The processor unit is mounted on horizontal DIN-rails using a unique slide-and-lock mechanism and can be fitted with a removable cover attached with screws. The 24 V DC power supply is connected to the TP830 Baseplate, powering all units on the CEX-Bus and Electrical ModuleBus.
3. Key Functions and Features
3.1 Processing and Storage Performance
Microprocessor: Utilizes the MPC866 running at 133 MHz, providing powerful instruction processing capability. Its performance is approximately 1.4 times that of the PM864.
Memory System:
64 MB SDRAM: For running the system and application programs.
4 MB Flash PROM: For firmware storage.
Memory Backup: Supports backup of memory content via an internal battery or external battery units (SB821 or SB822), ensuring data and program retention during power loss.
Compact Flash Interface: Supports loading of applications and storage of cold retain data via a CF card, facilitating program updates and data archiving.
3.2 Communication and Expansion Capabilities
The PM866 offers a flexible and powerful communication architecture:
3.3 Redundancy Functionality
The PM866 supports Processor Unit Redundancy, belonging to the redundant-capable series along with PM861, PM864, PM865, and PM891.
Redundant Configuration: The system contains two PM866 processor units, one acting as the Primary Controller and the other as the Backup Controller (hot stand-by).
Bumpless Switchover: If a fault occurs in the primary controller, the system performs a bumpless switchover in less than 10 milliseconds, with the backup controller taking over control tasks. Process outputs are frozen during the switchover.
Online Maintenance: A faulty processor unit (whether primary or backup) can be replaced while the system is running. Redundancy is restored after replacement.
Synchronization Mechanism:
The two processor units are connected via an RCU Link Cable (max. 1 m).
They are both connected to the same CEX-Bus, and either one can control the expansion units.
Employs a fault tolerance principle based on rollback points. The primary controller periodically establishes rollback points containing the complete processor state (registers + data memory) during execution and logs data memory changes since the last rollback point into a log buffer. At the rollback point, this log data is transferred to the backup controller, synchronizing its state with the primary.
If the primary fails, the backup resumes execution from the last rollback point. By reusing the results of already-executed peripheral operations, it ensures no impact on process I/O (communication units on the CEX-Bus).
Memory Protection: The processor unit's RAM features an automatic double-inverted memory function for detecting arbitrary bit errors in memory. All memory updates are written to both the primary and inverted memory in parallel, and compared on every read cycle. A mismatch forces a switchover.
Network Address Handling: In a redundant configuration, to ensure a bumpless switchover for the control network, the MAC and IP addresses are swapped between the initial primary and backup CPUs. Regardless of which CPU module acts as primary, the redundant controller is always identified by the same set of addresses, making the switchover transparent to other devices on the network.
3.4 I/O Connection and System Expansion
As shown in its functional block diagram, the PM866 manages the Optical and Electrical ModuleBus via its internal ModuleBus controller and expansion communication via the CEX-Bus controller. This architecture allows flexible configuration of the I/O system based on application needs:
Direct Local I/O: Connect S800 I/O via Electrical/Optical ModuleBus.
Remote/Distributed I/O: Connect via fieldbuses like PROFIBUS DP, FF HSE, etc.
Hybrid Systems: Multiple I/O connection methods can be used simultaneously.
Redundant I/O Connection: In redundant systems, S800 I/O units are connected to both CPUs via the Optical ModuleBus and two TB840 Cluster Modems on each I/O cluster. The built-in Electrical ModuleBus on the TP830 Baseplate cannot be used in redundant systems.
3.5 Power Supply and Diagnostics
Power Input: 24 V DC nominal (range 19.2 - 30 V DC), connected via a four-pin screw terminal.
Redundant Power Supply Monitoring: Provides SA and SB status inputs for monitoring redundant power supply status.
Internal Power Reservoir: Has an internal 5ms power reservoir, sufficient for the CPU to perform a controlled shutdown.
LED Status Indicators: The front panel provides multiple sets of LED indicators for quick diagnosis of unit and channel status, simplifying troubleshooting.
Protection Rating: IP20, suitable for installation inside enclosures.
4. Application Scenarios
With its high performance, high reliability, and powerful expansion capabilities, the PM866 Processor Unit is suitable for a wide range of industrial automation control fields:
Distributed Control Systems (DCS): Acts as a local control station in a DCS, handling complex analog and digital control loops.
High-Availability Applications: In critical industries like oil & gas, chemicals, and power, its redundancy functionality is used to build uninterrupted control systems.
Batch and Process Control: Suitable for continuous and batch processes requiring fast response and complex logic processing.
Large Machinery Control: Can serve as the main controller for large production lines or heavy machinery.
Integration of Multiple Buses: Acts as a core gateway and controller in hybrid systems requiring the integration of various fieldbuses and industrial Ethernet protocols such as PROFIBUS DP, FOUNDATION Fieldbus, Modbus TCP, and EtherNet/IP.
