PLC Instructions 2 IITD

8/13/2019 PLC Instructions 2 IITD

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Programmable Logic controller 1

Programmable

Logic Controllers


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PLC File Structure



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Comparison Instructions

Use these input instructions when you want tocompare values of data.

EQU: Test whether two values are equal (=)

NEQ: Test whether one value is not equal to a

second value (>


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Use these input instructions when you want tocompare values of data.

GEQ: Test whether one value is greater than or

equal to a second value (=>)

MEQ: Test portions of two values to see whether

they are equal

LIM: Test whether one value is within the limit range

of two other values



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EQU [Equal] This input instruction is true when

Source A = Source B.

The EQU instruction compares two userspecified values. If the values are

equal, it allows rung continuity. The

rung goes true and the output is

energized

You must enter a word address for

Source A. You can enter a program

constant or a word address for Source

B.



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NEQ [Not Equal] Use the NEQ instruction to test whether

two values are not equal.

If Source A and Source B are not equal,

the instruction is logically true. If the two

values are equal, the instruction is

logically false.

Source Amust be a word address.

Source Bcan be a word address or

program constant



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LEQ [Less Than or Equal] This conditional input instruction tests

whether one value (source A) is less

than or equal to another (source B).

If the value at source A is less than or

equal to the value at source B, the

instruction is logically true.

If the value at source A is greater than

the value at source B, the instruction islogically false.



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GRT [Greater Than] This input instruction compares two

user specified values.

If the value stored in Source A is

greater than the value stored in Source

B, it allows rung continuity. The rung

will go "true" and the output will be

energized (provided no other

instructions affect the rung's status). If the value at Source A is less than or

equal to the value at Source B, the

instruction is logically false.



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GEQ [Greater Than or Equal To] If the value stored in Source A is

greater than or equal to the value

stored in Source B, it allows rung

continuity. The rung will go true and theoutput will be energized (provided no

other instructions affect the rung's

status).

If the value at Source A is less than thevalue at Source B, the instruction is

logically false.



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MEQ [Masked Equal] This conditional instruction compares

16-bit data of a source address to 16-bit

data at a reference address through a

mask.

If the values match, the instruction is

true.

This instruction allows portions of the

data to be masked by a separate word.



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LIM [Limit Test] Use the LIM instruction to test for

values within or outside a specified

range, depending on how you set the

limits. The instruction is true when the Test

value is between the limits or is equal to

either limit.

If the Test value is outside the limits,the instruction is false.



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Program Control Instructions

Use these instructions to change the order inwhich the processor scans a ladder program.

Typically these instructions are used to minimize

scan time, create a more efficient program, and to

troubleshoot a ladder program.

JMP, LBL: Jump forward/backward to a corresponding

label instruction

JSR, SBR, RET: Jump to a designated subroutine and

return



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Control Instructions

JMP [Jump to Label] When the rung condition for this output

instruction is true, the processor jumps

forward or backward to the corresponding

label instruction (LBL) and resumes

program execution at the label.

More than one JMP instruction can jump

to the same label.

Jumping forward to a label saves

program scan time by omitting a program

segment until needed.

Jumping backward lets the controller

execute program segments repeatedly.



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LBL [Label] This input instruction is the target of the

JMP instruction having the same label

number.

You must program this instruction as thefirst instruction of a rung. This instruction

has no control bits. It is always evaluated

as true or logic 1.

You can program multiple jumps to the

same label by assigning the same label

number to multiple JMP instructions, but

assigning the same label number to two

or more labels causes a compile time

error.



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JSR [Jump to Subroutine] When rung conditions are true for this

output instruction, it causes the

processor to jump to the targeted

subroutine file. You can only jump to the first

instruction in a subroutine.

Each subroutine must have a unique

file number (decimal, 3-255).



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SBR [Subroutine] Use a subroutine to store recurring

sections of program logic that must

be executed from several points

within your application program. A subroutine saves memory because

you program it only once.

The instruction must be programmed

as the first instruction of the first rungof a subroutine.

Use of this instruction is optional, but

recommended.



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RET [Return] This output instruction marks the end

of subroutine execution or the end of

the subroutine file.

It causes the processor to resumeexecution in the main program file at

the instruction following the JSR

instruction where it exited the

program.



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RET [Return] The rung containing the RET

instruction may be conditional if this

rung precedes the end of the

subroutine. In this way, the processoromits the balance of a subroutine

only if its rung condition is true.

Without a RET instruction, the END

statement (always present in thesubroutine) automatically returns

program execution to the JSR

instruction in your calling ladder

program.Programmable Logic controller 19

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