Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 171)

Using Data Handling Instructions
9–23
FIFO and LIFO Instructions Overview
FIFO instructions load words into a file and unload them in the same order as they
were loaded. The first word in is the first word out.
LIFO instructions load words into a file and unload them in the opposite order as
they were loaded. The last word in is the first word out.
Entering Parameters
Enter the following parameters when programming these instructions:
•
Source is a word address or constant (–32,768 to 32,767) that becomes the next
value in the stack.
•
Destination (Dest) is a word address that stores the value that exits from the
stack.
This Instruction: Unloads the Value from:
FIFO’s FFU First word
LIFO’s LFU The last word entered
•
FIFO/LIFO is the address of the stack. It must be an indexed word address in
the bit, input, output, or integer file. Use the same FIFO address for the
associated FFL and FFU instructions; use the same LIFO address for the
associated LFL and LFU instructions.
•
Length specifies the maximum number of words in the stack. Address the
length value by mnemonic (LEN).
•
Position is the next available location where the instruction loads data into the
stack. This value changes after each load or unload operation. Address the
position value by mnemonic (POS).
Programming