Page 235 - Programmable Logic Controllers, Fifth Edition - Mobile version

L1 Inputs Ladder logic program • The OSR instruction ensures that the copy in-
struction is executed only once on a false-to-true
PB1 COP transition of the selector switch. In this way, if
COPY FILE
PB1 Source #N10:0 making the same recipe over a long period of time,
Destination #N12:0 the recipe needs to be copied only one time, not at
Length 4 every scan.

PB2 PB2 FLL 10.3 Data Compare Instructions

FILL FILE Data transfer operations are all output instructions,
Source 0
Destination #N12:0 whereas data compare instructions are input instructions.
Length 4 Data compare instructions are used to compare numerical
values. These instructions compare the data stored in two
Figure 10-17 Using the FLL instruction to change all the or more words (or registers) and make decisions based on
data in a file to zero.
the program instructions. Numeric values in two words
of memory can be compared for each of the basic data
Figure 10-18 is an example of the copy (COP) instruc- compare instructions shown in Figure 10-19, depending
tion used as part of a PLC drink-manufacturing program. on the PLC.
The operation of the program can be summarized as Data comparison concepts have already been used with
follows: the timer and counter instructions. In both these instructions,
• A three-position selector switch is used for drink
selection.
• Each selector switch position is electrically isolated Name Symbol
so that only one input circuit can be energized at Equal to (=)
any one time. Not equal to ( )
• Each of the three selector switch inputs is wired to Less than (<)
its corresponding input module address. Greater than (>)
Less than or equal to ( )
• Each recipe uses 5 memory words. Greater than or equal to ( )
• Depending on the type of drink selected, the recipe
is copied to the common working register #N7:50. Figure 10-19 Basic PLC data compare instructions.

Ladder logic program

Lime 1 B3:0/0
L1 Inputs COP
OSR COPY FILE
Source #N12:0
Destination #N7:50
Length 5
Lime 1
Cola 2 Cola 2 B3:0/1
COP
Cherry 3 OSR COPY FILE
Source #N12:5
Destination #N7:50
1 Length 5

2
Cherry 3 B3:0/2
3 COP
OSR COPY FILE
Selector switch Source #N12:10
Destination #N7:50
Length 5

Figure 10-18 The copy (COP) instruction used as part of a PLC drink-
manufacturing program.

216 Chapter 10 Data Manipulation Instructions

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