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DVP-ES2/EX2/SS2/SA2/SX2/SE Operation Manual - Programming

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1.7 Fuzzy Syntax

Generally, the ladder diagram programming is conducted according to the “up to down and left to

right” principle. However, some programming methods not following this principle still perform 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 Better and OK method is the ANB operation conducted by MPU. ANB instruction cannot

be used continuously for more than 8 times. If more than 8 ANB instructions are used continuously,

program error will occur. Therefore, apply ANB instruction after a block is made is the better

method to prevent the 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

The difference between Good and Bad method is very clear. With longer program code, the

required MPU operation memory increases in the Bad method. To sum up, following the general

principle and applying good / better method when editing programs prevents possible errors and

improves program execution speed as well.

Common Programming Errors

PLC processes the diagram program from up to down and left to right. When editing ladder

diagram users should adopt this principle as well otherwise an error would be detected by WPLSoft

when compiling user program. Common program errors are listed below:

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