PM861/PM864/TP830 Processor Unit – Redundancy Section 1 Introduction
36 3BSE 027 941 R301
PM861/PM864/TP830 Processor Unit – Redundancy
Processor unit redundancy is available. In this case, the controller contains two
processor units, each including memory for system and application software. One
unit is acting as primary, the other is backup (hot stand-by). The primary processor
unit controls the process. The backup stands by to take over in case of a fault in the
primary. The changeover is done bumplessly and in less than 10 ms. During the
changeover, the process outputs are frozen.
Following a changeover, the system operates as a system without redundancy with
only one processor unit in operation. You can replace the malfunctioning processor
unit while the system is running. After the replacement is carried out, the system
once again has a redundant processor unit.
If an error arises in the backup unit, you can also replace the backup unit while the
system is running.
Errors which occur in the backup unit can never affect the primary unit’s operation.
The primary unit and the backup unit are logically separated from one another.
Hardware errors in the primary processor unit cause the system to perform a correct
changeover. These hardware errors are "single errors".
The application programming and the communication are totally unaffected by the
redundancy.
The serial port, COM3 on the baseplate TP830, can not be used in redundant CPU
configuration.
The PM861/PM864 has an RCU Link Connector for connecting the RCU Link
Cable (see Figure 2 on page 29). In a redundant system the two processor units are
linked together with the RCU Link Cable. Both processor units are also connected
to the same CEX-bus and either of the two can control the expansion units
(see Figure 16 on page 66).
S800 I/O units are connected to the two CPUs via the optical ModuleBus and two
TB840 cluster modems on each S800 I/O cluster (see Figure 29 on page 98). The
built-in electrical ModuleBus on the TP830 baseplate cannot be used for connecting
S800 I/O in a redundant system.
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