07 programming program control instructions Training PLC Allen Bradley

PROGRAM CONTROL INSTRUCTIONS Instruction Function Description MCR Disable all the rungs in a section of logic JMP, LBL Jump over a section of logic that does not always need to be execu

DAY 2

SESSION 3

LADDER LOGIC PROGRAMMING – CONTROL

INSTRUCTIONS

PROGRAM CONTROL

INSTRUCTIONS

Instruction Function (Description)

MCR Disable all the rungs in a section of logic

JMP, LBL Jump over a section of logic that does not always need

to be executed JSR, SBR, RET Jump to a separate routine, pass data to the routine,

execute the routine, and return results.

TND Mark a temporary end that halts routine execution.

AFI Disable a rung.

SFR* Reset a sequential function chart (SFC)

MCR – MASTER CONTROL RESET

• The MCR instruction, used in pairs, creates a program zone that can

disable all rungs within the MCR instructions.

• When the MCR zone is enabled, the rungs in the MCR zone are scanned

for normal true or false conditions

• When disabled, the controller still scans rungs within an MCR zone, but

scan time is reduced because all the outputs in the zone are disabled.

• When the MCR zone is disabled, the rung-condition-in is false for all the

instructions inside of the MCR zone.

• When you program an MCR zone, note that:

• User must end the zone with an unconditional MCR instruction.

• User cannot nest one MCR zone within another.

• Do not jump into an MCR zone If the zone is false, jumping into the zone

activates the zone from the point to which user jumped to the end of the zone.

• If an MCR zone continues to the end of the routine, user do not have to

program an MCR instruction to end the zone.

SAMPLE PROGRAM OF MCR

JMP – JUMP DAN LBL – LABEL

• The JMP and LBL instructions skip portions of ladder logic.

• When enabled, the JMP instruction skips to the referenced LBL instruction and

the controller continues executing from there

• When disabled, the JMP instruction does not affect ladder execution.

JSR – JUMP TO SUBROUTINE, SBR

– SUBROUTINE, AND RET - RETURN

• The JSR instruction jumps execution to a different routine

• The SBR instruction passes data to and executes a routine

• The RET instruction returns the results.

• The JSR instruction initiates the execution of the specified

routine, which is referred to as a subroutine:

• The subroutine executes one time

• After the subroutine executes, logic execution returns to the

routine that contains the JSR instruction

SAMPLE PROGRAM

s c a n

s c a n

Program constant and value are saved in logical address that passed to SBR instruction when JMP being executed to subroutine file

Next, when subroutine finish,

parameter value return to JSR by

RET instructions

SUBROUTINE WHICH CONNECTED

There are no restrictions, other than controller memory, on the

number of nested routines user can have, or the number of

parameters user pass or return.

JSR SBR

JSR

RET

SBR

JSR

RET

SBR

RET

Main Program

U:2

U:3 U:4 U:5

TND – TEMPORARY END

• The TND instruction acts as a boundary.

• When enabled, the TND instruction lets the controller execute

logic only up to this instruction.

• When enabled, the TND instruction acts as the end of the

routine

• When the controller scans a TND instruction, the controller

moves to the end of the current routine

• If the TND instruction is in a subroutine, control returns to the

calling routine

• If the TND instruction is in a main routine, control returns to

the next program within the current task.

SAMPLE PROGRAM OF TND

This rung will be act as

END instruction in the end

of program

If I:000/5 goes true, then

TND will be enable and will

be cause the rest rungs will

not be scanned.

AFI – ALWAYS FALSE

• The AFI instruction sets its rung-condition-out to false.

• Use the AFI instruction to temporarily disable a rung while you

are debugging a program.

• When enabled, the AFI disables all the instructions on this

rung.

SAMPLE PROGRAM

Always false

EOT - END OF TRANSITION

• The EOT instruction returns a Boolean state to an SFC

instruction.

• Because the EOT instruction returns a Boolean state, multiple

SFC routines can share the same routine that contains the

EOT instruction

• If the calling routine is not a transition, the EOT instruction

acts as a TND instruction.

• Sample Program of :

UID – USER INTERRUPT DISABLE

The UID instruction and the UIE instruction work together to

prevent a small number of critical rungs from being interrupted

by other tasks.

Sample Program of UID :

Interruptible program

Uninterruptable program

SESSION 4

LADDER LOGIC PROGRAMMING – MATH

INSTRUCTIONS