Stop Mode - Siemens SIMATIC S7-400H System Manual

Explanation of the figure
Point Description
1. After the power supply has been turned on, the two CPUs (CPU 0 and CPU 1) are in STOP state.
2. CPU 0 changes to the STARTUP state and executes OB 100 or OB 102 according to the startup mode; see
also section STARTUP mode (Page 132).
3. If startup is successful, the master CPU (CPU 0) changes to standalone 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 tag
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 modes (Page 133).
5. After a successful link-up, updating is started, see section Update sequence (Page 149). The master CPU
updates the dynamic data of the standby CPU. Dynamic data includes inputs, outputs, timers, counters, bit
memories and data blocks.
Following the update, the memories of both CPUs have the same content; see also section LINK-UP and
UPDATE modes (Page 133).
6. The master and standby CPUs are in RUN after the update. Both CPUs process the user program in
synchronous mode.
Exception: Master/standby changeover for configuration/program modifications.
The redundant system state is only supported with CPUs of the same version and firmware version.
11.3.1

STOP mode

Except for the additions described below, the behavior of S7-400H CPUs in STOP state
corresponds to that of standard S7-400 CPUs.
When you download a configuration to one of the CPUs while both are in STOP state,
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.
S7-400H
System Manual, 03/2012, A5E00267695-11
master mode.
CPU to which an active connection exists, regardless of the master or standby status.
NOTICE
A system startup may trigger a master–standby changeover.
A fault-tolerant CPU can only exit the STOP state with a loaded configuration.
System and operating states of the S7–400H
11.3 The operating states of the CPUs
131