Siemens SIMATIC S7-400H, Системное руководство

Страница: 122 / 504

System and operating states of the S7–400H
11.1 Introduction
S7-400H
122
System Manual, 03/2012, A5E00267695-11
Master/reserve assignment
When the S7-400H is initially switched on, the CPU that started up first assumes master
mode, and the partner CPU assumes reserve mode.
The preset master/reserve assignment is retained when both CPUs power up
simultaneously.
The master/reserve assignment changes when:
1.
The reserve CPU starts up before the master CPU (interval of at least 3 s)
2. The master CPU fails or goes into STOP in redundant system mode
3. No error was found in ERROR-SEARCH mode (see also section ERROR-SEARCH mode
(Page 135))
4. Programmed master-standby switchover with SFC 90 "H_CTRL"
Synchronizing the subsystems
The master and reserve CPUs are linked by fiber-optic cables. Both CPUs maintain event-
synchronous program execution via this connection.
6XEV\VWHP&38
6\QFKURQL]DWLRQ
6XEV\VWHP&38
Figure 11-1 Synchronizing the subsystems
Synchronization is performed automatically by the operating system and has no effect on the
user program. You create your program in the same way as for standard S7-400 CPUs.
Event-driven synchronization procedure
The "event-driven synchronization" procedure patented by Siemens was used for the S7-
400H. This procedure has proved itself in practice and has already been used for the S5-
115H and S5-155H controllers.
Event-driven synchronization means that the master and reserve always synchronize their
data when an event occurs which may lead to different internal states of the subsystems.
The master and reserve CPUs are synchronized when:
●
There is direct access to the I/O
● Interrupts occur
● User timers (e.g. S7 timers) are updated
● Data is modified by communication functions