Siemens SIMATIC S7-400H Manual page 39

Explanations relating to Figure 4-2
Table 4-2
Item
1.
2.
3.
4.
5.
6.
4.3.1 STOP Operating Mode
Except for the additions described below, the CPUs of the S7-400H behave in
exactly the same way in STOP mode as the standard CPUs on the S7-400 do.
When both CPUs are in STOP mode and you want to load a configuration, you
must make sure you load it into the master CPU. Only then are the system data
blocks transferred to the I/O modules.
Memory Reset
Memory Reset always affects only that CPU to whose function it is applied. If you
want to reset both CPUs, you must do so first for one and then for the other.
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Explanations Relating to Figure 4-2 System and Operating Modes of the
Fault-tolerant System
Once the power supply has been turned on, the two CPUs (CPU 0 and
CPU 1) are in the STOP mode.
CPU 0 goes to the STARTUP mode and processes OB 100 or OB 102,
depending on the type of startup.
(Refer to Section 4.3.2)
If startup has been successful, the master CPU (CPU 0) changes to Solo
mode (the master CPU processes the user program on its own).
If the standby CPU (CPU 1) requests LINK-UP, the master and standby
CPUs compare their user programs. If they establish differences, the
master CPU updates the user program of the standby CPU.
(Refer to Section 4.3.3)
After a successful link-up the update starts (see section 5.2.2). In this
instance the master CPU updates the dynamic data of the standby CPU
(dynamic data are inputs, outputs, timers, counters, memory markers
and data blocks).
The contents of the memories of both the CPUs are identical following
updating.
(Refer to Section 4.3.3)
The master and standby CPUs are at RUN following updating. The two
CPUs process the user program in synchronism.
Exception: in the case of master/standby switch-over for
configuration/program modifications.
The Redundant system mode is only possible if both CPUs are of the
same release and the same firmware version.
System and Operating Modes of the S7-400H
Description
4-7