Installation manual
CNC 8035
INTRODUCTION TO THE PLC
PLC program execution
7.
(SOFT M: V15.3X)
(S
OFT T: V16.3X)
·289·
The following example shows how the PLC acts when working with real or image values.
As can be observed, the system is faster when operating with real resource values.
Operating with image values permits analyzing the same resource along the whole program with
the same value regardless of its current (instantaneous) real value.
Operating with real values
In the first scan, when execution the instruction M1 = M2, M1 has a real value of “1” set by the previous
instruction.
The same is true for instructions M2=M3 and M3=O5
That is why real values are used, output O1 takes the value of “1” in the first scan.
Operating with image values
The first cycle (scan) sets the real value of M1=1; but its image value will not be set to "1" until the
end of the cycle.
In the 2nd cycle (scan), the image value of M1 is "1" and the real value of M2 is set to "1"; but the
image value of M2 will not be set to "1" until the end of the cycle.
In the 3rd cycle (scan), the image value of M2 is "1" and the real value of M3 is set to "1"; but the
image value of M3 will not be set to "1" until the end of the cycle.
In the 4th cycle (scan), the image value of M3 is "1" and the real value of O5 is set to "1".
PLC program () = M1 Assigns the value of “1” to mark M1.
M1 = M2 Assigns the value of M1 to M2.
M2 = M3 Assigns the value of M2 to M3.
M3 = O5 Assigns the value of M3 to output O5.
Scan 1
Scan 4
Scan 3
Scan 2
M1 M2 M3 O5 M1 M2 M3 O5
11111111
11111110
11111100
11111000
00000000
REA IMA
()=M1
M3 = O5
M2 = M3
M1 = M2
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