Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 187)

Publication 1747-UM010B-EN-P - September 2003
M0-M1 Files and G Files B-7
In the equivalent rungs of the figure below, XIC instruction M0:2.1/1
is used only in rung 1, reducing the SLC 5/02 scan time by
approximately 1 ms.
The following figure illustrates another economizing technique. The
COP instruction addresses an M1 file, adding approximately 4.29 ms
to the scan time if you are using a SLC 5/02 Series B processor. Scan
time economy is realized by making this rung true only periodically,
as determined by clock bit S:4/8. (Clock bits are discussed in the
SLC 500 Instruction Set Reference Manual, publication number
1747-RM001.) A rung such as this might be used when you want to
monitor the contents of the M1 file, but monitoring need not be on a
continuous basis.
Capturing M0-M1 File Data
The first two ladder diagrams in the last section illustrate a technique
allowing you to capture and use M0 or M1 data as it exists at a
particular time. In the first figure, bit M0:2.1/1 could change state
between rungs 1 and 2. This could interfere with the logic applied in
rung 2. The second figure avoids the problem. If rung 1 is true, bit
B3/10 captures this information and places it in rung 2.
In the second example of the last section, a COP instruction is used to
monitor the contents of an M1 file. When the instruction goes true,
the 6 words of data in file #M1:4.3 is captured as it exists at that time
and placed in file #N10.0.
M0:2.1
1
B3
10
B3
14
B3
12
B3
10
These rungs provide equivalent operation to
those of figure A by substituting XlC
instruction B3/10 for XlC instruction M0:2.1/1
in rung 2. Scan time is reduced by
approximately 1 ms (Series B processor).
COP
Copy File
Source
#M1:4.3
Dest #N10:0
Length 6
COP S:4
8
B11
0
OSR
S:4/8 causes the #M1:4.3 file to
update the #N10:0 file every
2.56 seconds.