ELC Programming Manual
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Fuzzy Syntax
Generally, the ladder diagram programming is scanned “top to bottom and left to right”. However,
some programming methods do not follow this principle and still deliver the same control results.
Here are some examples explaining this kind of “fuzzy syntax.”
Example 1:
Better method OK method
LD X0 LD X0
OR X1 OR X1
LD X2 LD X2
OR X3 OR X3
ANB LD X4
LD X4 OR X5
OR X5 ANB
X0 X2 X4
X5X3X1
ANB ANB
The two instruction programs can be converted into the same ladder diagram. The difference
between the Better and the OK method is the ANB operation. The ANB instruction cannot be used
continuously more than 8 times. If more than 8 ANB instructions are used continuously, a program
error will occur. Therefore, applying the ANB instruction after a block is made is the better method
to prevent possible errors. In addition, it’s also the more logical and clearer programming method
for general users.
Example 2:
Good method Bad method
LD X0 LD X0
OR X1 LD X1
OR X2 LD X2
OR X3 LD X3
ORB
ORB
X0
X1
X2
X3
ORB
The difference between the Good and the Bad method is very clear. With longer program code, the
required memory increases in the Bad method. Following the general principle and applying good /
better methods when editing programs prevents possible errors and improves program execution
speed as well.
Common Programming Errors
The ELC processes the diagram program from top to bottom and left to right. When editing ladder
diagrams users should adopt this principle as well or an error would be detected by ELCSoft when
compiling the user program. Common program errors are listed below:
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