Overview

The PM891 is a monolithic processor unit that integrates the power supply, CPU boards, and termination circuitry into a single compact assembly. It is designed for high-performance control applications within the AC 800M system family, offering strong processing capability and high availability through extensive redundancy features.

Hardware Architecture

The unit includes the following integrated components:

Microprocessor with onboard RAM memory

Real-time clock

LED status indicators

INIT push button for system initialization

Secure Digital (SD) interface for storage and firmware handling

No internal battery (battery-less architecture)

Communication Ports

2 × RJ45 Ethernet ports (CN1, CN2):
For Control Network connectivity, supporting redundant configurations

1 × RJ45 Serial Port (COM4):
Electrically isolated and dedicated for configuration tools

The PM891 supports full CPU redundancy, covering:

CPU module

CEX-Bus

Communication interfaces

S800 I/O connections

This ensures high availability in critical process control environments.

Communication Expansion (CEX-Bus)

A fully integrated CEX-Bus expands the controller’s native communication capabilities through additional interface modules. The system supports:

Redundant communication interfaces on the CEX-Bus

Increased availability using the BC810 Interconnection Unit, which divides the CEX-Bus into isolated segments to prevent propagation of communication failures

Optical Modulebus

The PM891 also includes an optical Modulebus, enabling:

Connection of up to seven clusters of S800 I/O units

Each cluster supporting up to 12 I/O units

Every PM891 is assigned a unique Ethernet hardware address for secure and traceable identification within the control network.

Features and Benefits

High Reliability: Simplified diagnostic functions support efficient fault identification.

Modular Design: Allows flexible, step-by-step system expansion.

IP20 Protection Class: Suitable for installation without an enclosure.

Full EMC Certification: Ensures robust performance in industrial environments.

High Performance & Large Application Memory: Supports demanding control applications.

Segmented CEX-Bus: Achieved using a pair of BC810 units for improved availability.

Built-in Redundant Ethernet Ports: Enhances network fault tolerance and system uptime.