Section 1 Introduction PM891/PM86x/TP830 Processor Unit – Redundancy
3BSE036351-510 A 47
PM891/PM86x/TP830 Processor Unit – Redundancy
Processor unit redundancy is available for PM861, PM864, PM865, PM866, and
PM891. 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, ready 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.
PM86x/TP830 Redundancy
The PM861/PM864/PM865/PM866 has an RCU Link Connector for connecting the
RCU Link Cable (see Figure 2 on page 32). In a redundant system the two processor
units are linked together with the RCU Link Cable (max 1 m). Both processor units
are also connected to the same CEX-Bus and either of the two can control the
expansion units (see Figure 29 on page 93).
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 55 on page 161). The
built-in electrical ModuleBus on the TP830 baseplate cannot be used for connecting
S800 I/O in a redundant system.
The serial port, COM3 on the baseplate TP830, cannot be used in redundant CPU
configuration.
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