Programmable Logic Controllers

Chapter

14Data Handling Instructions

Files

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Objectives

• Use PLC instructions for moving data from one register to another.

• Create stacks for storing and retrieving data from PLC memory.

• Move data between tables.• Use PLC instructions for number system

conversion.

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

Data Handling Instructions

• Reading, storing, retrieving, and writing of data on ports and registers.

• Moving or copying data to another register or file.

• Converting data to a different number system.

• Performing a logic operation on data.

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Data Handling Instructions (Cont.)

• Move (MOV).• Masked move

(MVM).• FIFO load (FIFO).• FIFO unload (FFU).• LIFO load (LIFO).• LIFO unload (LFU).• Copy file (COP).• Fill file (FLL).

• Convert to BCD (TOD).• Convert from BCD

(FRD).• Convert from radians to

degrees (DEG).• Convert from degrees

to radians (RAD).

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Index Register

• Sometimes simply called a pointer.• A register that holds an address of a

data. • Used to move a word into a specific

address.• Data is placed in another data register.

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FIFO and LIFO

• Like pallets, data registers can be stored and retrieved in two different ways:– First-in-first-out (FIFO).– Last-in-first-out (LIFO).

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FIFO and LIFO (Cont.)

• Concept of storing and retrieving pallets is similar to the way data is placed in and retrieved from a stack.

• A stack in PLC or computer terms:– A group of consecutive data registers, or

words, placed temporarily in a memory location, or buffer.

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

FIFO and LIFO (Cont.)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

FIFO and LIFO (Cont.)

• When stacking data: – Stack grows larger as data registers are

placed in stack.– Stack grows smaller as data registers are

retrieved from stack.

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

FIFO and LIFO (Cont.)

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

FIFO and LIFO (Cont.)

• In FIFO operation, first item in stack is first item out of stack.

• In LIFO operation, last item in stack is first item out of stack.

• Push operation – placing an item in a stack.

• Pop operation – retrieving an item from a stack.

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

FIFO and LIFO (Cont.)

• Allen-Bradley SLC 500 PLCs have four instructions for LIFO and FIFO operations:– FIFO load (FFL).– FIFO unload (FFU).– LIFO load (LFL).– LIFO unload (LFU).

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

FIFO and LIFO (Cont.)

• In PLC systems, stacks are created when stacks of integer words (i.e., double-byte data) are stored in the memory buffer.

• Data can be transferred into a register or another memory location from the stack.

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

FFL Load Instruction

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LFL Load Instruction

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Copy File and Fill File Instructions

• Data handling instructions used to store blocks of data in a PLC file:– Copy file (COP).– Fill file (FLL).

• Can use these instructions to manually enter a file with constant numbers or data from another file.