plc programming a to z

1. 10-1
Dr. D. J. Jackson Lecture 10-1Electrical & Computer Engineering
Programmable Logic
Controllers
File (Queue) Instructions
Dr. D. J. Jackson Lecture 10-2Electrical & Computer Engineering
File Instruction Types
• FFL - First In, First Out (FIFO) Load
• FFU - First In, First Out (FIFO) Unload
• LFL - Last In, First Out (LIFO) Load
• LFU - Last In, First Out (LIFO) Unload

2. 10-2
Dr. D. J. Jackson Lecture 10-3Electrical & Computer Engineering
FIFO Load Instruction
• On a false-to-true rung
transition, the FFL
instruction loads words
or long words into a
user-created file called
a FIFO stack.
Dr. D. J. Jackson Lecture 10-4Electrical & Computer Engineering
FIFO Load Operands
• Source - The source operand is a constant or
address of the value used to fill the currently
available position in the FIFO stack.
– The address level of the source must match the FIFO stack.
If FIFO is a word size file, source must be a word value or
constant. If FIFO is a long word size file, source must be a
long word value or constant. The data range for the source
is from -32768 to 32767 (word) or -2,147,483,648 to
2,147,483,647 (long word).
• FIFO - The FIFO operand is the starting address of
the stack.
• Control - This is a control file address. The status
bits, stack length, and the position value are stored
in this element.

3. 10-3
Dr. D. J. Jackson Lecture 10-5Electrical & Computer Engineering
FIFO Control Structure
• Length - The length operand contains the number of elements in the
FIFO stack to receive the value or constant found in the source. The
length of the stack can range from 1 to 128 (word) or 1 to 64 (long
word). The position is incremented after each load.
• Position - This is the current location pointed to in the FIFO stack. It
determines the next location in the stack to receive the value or
constant found in source. Position is a component of the control
register. The position can range from 0 to 127 (word) or 0 to 63 (long
word).
Dr. D. J. Jackson Lecture 10-6Electrical & Computer Engineering
FIFO Loading & Unloading

4. 10-4
Dr. D. J. Jackson Lecture 10-7Electrical & Computer Engineering
FIFO Unload Instruction
• On a false-to-true rung
transition, the FFU
instruction unloads words or
long words from a user-
created file called a FIFO
stack.
• The data is unloaded using
first-in, first-out order.
• After the unload completes,
the data in the stack is
shifted one element toward
the top of the stack and the
last element is zeroed out.
• FFU operands are exactly as
described in the FFL
instruction.
Dr. D. J. Jackson Lecture 10-8Electrical & Computer Engineering
LFL - Last In, First Out (LIFO) Load
• On a false-to-true rung
transition, the LFL
instruction loads words
or long words into a
user-created file called
a LIFO stack.
• This instruction’s
counterpart, LIFO
unload (LFU), is paired
with a given LFL
instruction to remove
elements from the LIFO
stack.

5. 10-5
Dr. D. J. Jackson Lecture 10-9Electrical & Computer Engineering
LIFO Loading & Unloading