Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM User Manual
Page 388
Publication AG-UM008C-EN-P - February 2005
E-6 Sample Ladder Logic
SLC DF1 Half-Duplex Slave and DF1 Radio Modem Report-by-Exception MSG
SLC DF1 Half-Duplex Slave "Report-By-Exception" MSG Logic
Copy all of the "live" discrete and analog values to be written as a "report-by-exception" MSG to the SLC Master into a data compare buffer, which is a contiguous block of words starting in
B3:0. This copying occurs continuously between successful MSG writes. If multiple changes occur after the MSG begins executing, and before the MSG has successfully completed, only
the last change will be recorded and sent during the next MSG execution. Care should be exercised with constantly changing analog data so that the MSG doesn't continously retrigger, thus
negating the efficiencies of a "report-by-exception" scheme. In this example, the SLC real time clock values (S:37 to 42) will be sent immediately upon any change of year, month, day, hour
or minute, or every15 seconds, whichever occurs first.
0000
N7:90
13
MSG
Done
COP
Copy File
Source
#S2:37
Dest
#B3:0
Length
6
COP
Data Compare Buffer
EN
DN
TON
Timer On Delay
Timer
T4:0
Time Base
1.0
Preset
15<
Accum
0<
TON
Max Delay Before
Retriggering MSG
If 15 seconds have elapsed since the last successful completion of the MSG write, snapshot the current data values for writing to the Master and retrigger the MSG (regardless of whether data
values have changed since the last write).
0001
T4:0
DN
Max
Delay
COP
Copy File
Source
#B3:0
Dest
#N7:0
Length
6
COP
MSG Write Buffer
U
N7:90
15
MSG
Enable
JMP
Q2:2
Jump to
MSG Rung
If the MSG is enabled, skip over the data comparison rungs directly to the MSG rung. If the MSG has just completed in error, retrigger the MSG immediately and jump directly to the MSG
0002
N7:90
13
MSG
Done
N7:90
12
MSG
Error
U
N7:90
15
MSG
Enable
JMP
Q2:2
Jump to
MSG Rung
The next three rungs create a data file comparison routine. This rung clears the index register (S:24) to prepare it for use in the Not Equal comparison instruction.
0003
CLR
Clear
Dest
S2:24
0<
CLR
Index Register
rung.