GFK-1527A Chapter 4 Normal Operation 4-13
4
Example
In the following example, when %M00035 is on, the input and output copies are disabled.
%M00035 %T00041
SVC_
REQ
FNC
PARM
CONST
00043
%L00001
MOVE_
INT
IN
LEN
00001
CONST
00001 Q %L00002
MOVE_
INT
IN
LEN
00001
CONST
00000 Q %L00001
Backup Qualification w ith SVCREQ #43
Service Request function block #43 can be used to help determine if the backup PLC unit is
collecting inputs properly (that is, validate the input scan). It can also be used to help determine
whether the backup PLC unit is calculating outputs and internal variables properly (that is, validate
the logic solution). Instructions are given below.
Validating the Backup PL C's Input Scan
To determine whether the backup PLC is collecting inputs properly, follow these steps:
1. Activate SVCREQ #43 on the backup CPU, passing “0, 1" to disable the input and output data
transfer copies.
2. Observe the backup unit' s %I and %AI reference tables. The valu es in th ese tables correspond
to the inputs that the backup is currently collecting.
3. Visually compare the backup unit's %I and %AI reference tables with the active unit's tables.
Pay special attention to the %I and %AI references that are configured to be shared between
the two units.
4. When you are satisfied that th e backup unit is collecting inpu t s pr oper ly, disable the rung that
calls SVCREQ #43.
Validating the Backup PLC's Logic Solution
To determine whether the backup PLC is calculating outputs and internal variables properly, follow
these steps:
1. Activate SVCREQ #43 on the backup CPU, passing “0, 2" to disable the output data transfer
copy.
2. Observe the backup unit's %Q, %AQ, %M, and %R reference tables. The values in these tables
correspond to the inputs that the backup is currently calculating.
3. Visually compare the backup unit's %Q, %AQ, %M, and %R reference tables with the active
unit's tables. Pay special attention to the %Q, %AQ, %M, and %R references that are
configured to be shared between the two units.
4. When you are satisfied that the backup unit is calculating outputs and internal variables
properly, disable the rung that calls SVCREQ #43.