Saia-Burgess Controls AG
User Manual Standby System
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Document 27-645
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Edition E
NG 02
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2017-04-26
Media Exchange
Diagnostic
2-8
2
2.4
Media Exchange
To communicate between CPU0 and CPU1 on each device, and between the
programs on the Primary and Secondary devices, media values can be transferred
cyclically between each CPU.
Special symbol files are used to define the media to be transferred between CPU0
and CPU1 of the Primary and Secondary devices and the media to be transferred
between the CPU1s of the Primary and Secondary devices. Two options are
available: “Single symbols file” and “Separate symbol files”, see the Standby
System Configuration dialog box.
If the same program is to be used in CPU0 of both devices (Primary and Secondary),
then the “Single symbols file” option must be used, so that the symbol names are always
the same in both programs.
Single symbol file
One symbol file (default name “RedSymbols.sy5”) is used. When a value is written
to one of the media addresses defined in this file, the value is transferred to the
other CPUs in the ACTIVE and the STANDBY devices.
The procedure is as follows:
1. CPU0 of the ACTIVE device modifies the media values of symbols defined
in “RedSymbols.sy5”, either by the user program, an S-Bus telegram, a Web
page, etc.
2. CPU0 transfers the modified media values to CPU1 of the ACTIVE device at
the end of the CPU1 cycle. (If CPU1’s program subsequently modifies the same
value before the end of the cycle, then the new value will be used instead of the
value modified by CPU0.)
3. All media values defined in ‘RedSymbols.sy5” are then cyclically copied back to
CPU0.
4. For data synchronization between the Active and Standby devices, all me-
dia values are transferred from CPU1 of the ACTIVE device to CPU1 of the
STANDBY device. This also transfers the media values that were modified by
CPU0 of the ACTIVE device.
5. All the “RedSymbols.sy5” media are cyclically transferred from CPU1 to CPU0
of the STANDBY device. This also transfers the media values that were modi-
fied by CPU0 of the ACTIVE device.