Link-Up And Update Modes; Run Mode; Table 11- 2 Causes Of Error Leading To Redundancy Loss - Siemens SIMATIC S7-400H System Manual

11.3.3

LINK-UP and UPDATE modes

The master CPU checks and updates the memory content of the reserve CPU before the
fault-tolerant system assumes redundant system mode. This is implemented in two
successive phases: link-up and update.
The master CPU is always in RUN mode and the reserve CPU is in LINK-UP or UPDATE
mode during the link-up and update phases.
In addition to the link-up and update functions, which are carried out to establish redundant
system mode, the system also supports linking and updating in combination with
master/reserve changeover.
For detailed information on link-up and updating, refer to section Link-up and update
(Page 141).
11.3.4

RUN mode

Except for the additions described below, the behavior of S7-400H CPUs in RUN mode
corresponds to that of standard S7-400 CPUs.
The user program is executed by at least one CPU in the following system states:
● Single mode
● Link-up, update
● Redundant
Single mode, link-up, update
In the system states standalone mode, link-up and update, the master CPU is in RUN and
executes the user program in standalone mode.
Redundant system mode
The master CPU and standby CPU are always in RUN when operating in redundant system
mode. Both CPUs execute the user program in synchronism, and perform mutual checks.
In redundant system mode it is not possible to test the user program with breakpoints.
The redundant system state is only supported with CPUs of the same version and firmware
version. Redundancy will be lost if one of the errors listed in the following table occurs.
Table 11- 2
Cause of error
Failure of one CPU
Failure of the redundant link (synchronization
module or fiber-optic cable)
RAM comparison error
S7-400H
System Manual, 03/2012, A5E00267695-11
Causes of error leading to redundancy loss
System and operating states of the S7–400H
11.3 The operating states of the CPUs
Reaction
Failure and replacement of a CPU (Page 266)
Failure and replacement of a synchronization
module or fiber-optic cable (Page 272)
ERROR-SEARCH mode (Page 135)
133