Stop Operating State - Siemens SIMATIC S7-400H System Manual

System and operating states of the S7-400H
8.4 The operating states of the CPUs
Explanation of the diagram
Point Description
1. After the power supply has been turned on, the two CPUs (CPU 0 and CPU 1) are in STOP mode.
2. CPU 0 changes to STARTUP and executes OB 100 or OB 102 according to the startup mode; see also
section STARTUP operating state (Page 85).
3. If startup is successful, the master CPU (CPU 0) changes to single mode. The master CPU executes the
user program alone.
At the transition to the LINK-UP system state, no block may be opened by the "Monitor" option, and no variable
table may be active.
4. If the standby CPU (CPU 1) requests LINK-UP, the master and standby CPUs compare their user programs.
If any differences are found, the master CPU updates the user program of the standby CPU; see also
section LINK-UP and UPDATE operating states (Page 85).
5. After a successful link-up, updating is started, see section Update sequence (Page 101). The master CPU
updates the dynamic data of the standby CPU. Dynamic data means inputs, outputs, timers, counters, bit
memory and data blocks.
Following the update, the memory of both CPUs has the same content; see also section LINK-UP and
UPDATE operating states (Page 85).
6. The master and standby CPUs are in RUN after the update. Both CPUs process the user program
synchronized with each other.
Exception: Master/standby changeover for configuration/program modifications.
The redundant mode is only supported when both CPUs are the same version and have the same firmware
version.
8.4.1

STOP operating state

Except for the additions described below, the behavior of S7-400H CPUs in STOP
corresponds to that of standard S7-400 CPUs.
When you download a configuration to one of the CPUs while both are in STOP, observe the
points below:
● Start the CPU to which you downloaded the configuration first, in order to set it up for
● By initiating the system startup request on the programming device, you first start the
Memory reset
The memory reset function affects only the selected CPU. To reset both CPUs, you must
reset one and then the other.
84
master mode.
CPU to which an online connection exists, regardless of the master or standby status.
NOTICE
A system startup may trigger a master-standby changeover.
System Manual, 09/2007, A5E00267695-03
S7-400H