Startup Operating Mode; Startup Processing By The Master Cpu; Operating States Link–Up And Update - Siemens SIMATIC S7-400H Manual

5.3.2

STARTUP Operating Mode

Except for the additions described below, the CPUs of the S7-400H behave in
exactly the same way in STARTUP mode as the standard CPUs on the S7-400 do.
Startup
The fault-tolerant CPUs distinguish between a cold restart and a reboot (warm
restart).
The restart is not supported by fault-tolerant CPUs.

Startup processing by the master CPU

The startup system mode of an S7-400H is processed entirely by the master CPU;
the standby CPU plays no part in startup.
At STARTUP the master CPU compares the existing I/O configuration with the
hardware configuration that you created with STEP 7. If there are differences, the
master CPU reacts in the same way a standard CPU would on the S7-400.
The master CPU checks and assigns parameters to the
1. switched I/O
2. one-way, single-channel I/O.
Further information
You will find detailed information on STARTUP mode in the Programming with
STEP 7 manual.
5.3.3 Operating States LINK–UP and UPDATE
Before the fault-tolerant system accepts redundant system mode the master CPU
checks and updates the memory contents of the standby CPU. (Exception: in the
case of link-up and update with subsequent switch-over to CPU with modified
configuration).
Checking and updating of the memory contents are performed in two phases which
run consecutively and will be referred to in the following as "link-up" and "update".
During link-up and update the master CPU is always at RUN and the standby CPU
is in LINK-UP or UPDATE mode.
When executing a link-up and update a distinction is made between whether
redundant system mode or a master/standby switch-over is to be achieved (for
master/standby switch-over for configuration modifications).
Detailed information on the link-up and update process can be found in Section 6.2
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
System and Operating Modes of the S7-400H
5-7