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4 |
Programming a Data Transfer from Backup Unit to Active Unit
Optionally, the program logic can be used in both CPUs to transfer eight bytes (4 registers) of data from the backup unit to the active unit before the next logic solution.
o initiate this transfer, the backup unit executes SVCREQ #27 (Write to Reverse Transfer Area). his command copies eight bytes of data from the reference in the backup unit specified by the
PARM parameter. Note that SVCREQ #27 only works when its CPU is the backup unit. When its CPU is the active unit, SVCREQ #27 has no effect.
he active unit stores the transferred data in a temporary buffer. The program in the active unit must include SVCREQ #28 (Read from Reverse Transfer Area), which copies the eight bytes of data from the temporary buffer to the reference specified by the PARM parameter. SVCREQ #28 only works in the active unit. It has no effect when its CPU is the backup unit.
here is always a
his data copied from the buffer is not valid in the following cases:
during the first scan after either unit has transitioned to RUN;
Twhile the backup unit is in STOP mode;
if the backup unit does not issue SVCREQ #27.
The data should not be used if REM_RDY is off or if REM_RDY is transitioning to on.
Data Transfer Example
The following rungs would be placed in the program logic of both units. In this example, the backup unit would send %P0001 through %P0004 to the active unit. The active unit would read the data into %P0005 through %P0008. %P0001 through %P0004 on the active unit and %P0005 through %P0008 on the backup unit would not change. %T0002 would be set to indicate that the operation was successful and that the data could be used.
REM_ RDY | %T00001 |
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REM_ACT
CONST 00027
%P00001
%T00001
%M00001
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| REQ |
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| PARM |
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| LOC_ACT |
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| %T00002 |
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| CONST |
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| 00028 |
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| %P0005 |
| PARM |
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Series |