Publication 1766-RM001A-EN-P - October 2008
File Instructions
277
FFL - First In, First Out
(FIFO) Load
Instruction Type: output
On a false-to-true rung transition, the FFL instruction loads words or long
words into a user-created file called a FIFO stack. This instruction’s
counterpart, FIFO unload (FFU), is paired with a given FFL instruction to
remove elements from the FIFO stack. Instruction parameters have been
programmed in the FFL - FFU instruction pair shown below.
This instruction uses the following 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…32767 (word) or
-2,147,483,648…2,147,483,647 (long word).
•
FIFO - The FIFO operand is the starting address of the stack.
EN
DN
EM
FFL
FIFO Load
Source
N7:0
FIFO
#N7:1
Control
R6:0
Length
1<
Position
0<
FFL
Execution Time for the FFL Instruction
Controller
Data Size
When Rung Is:
True
False
MicroLogix 1400
word
8.2970 µs
6.1730 µs
long word
9.0910 µs
7.4630 µs
(EU)
(EM)
(DN)
FFL
FIFO LOAD
Source
N7:10
FIFO
#N7:12
Control
R6:0
Length
34
Position
9
FFU
FIFO UNLOAD
FIFO
#N7:12
Dest
N7:11
Control
R6:0
Length
34
Position
9
(EN)
(DN)
(EM)
Destination
Position
N7:11
N7:12
0
N7:13
1
FFU instruction
unloads data from
stack #N7:12 at
position 0, N7:12
N7:14
2
3
4
5
34 words are allocated
for FIFO stack starting
at N7:12, ending at
N7:45
6
7
Source
8
N7:10
9
FFL instruction loads
data into stack
#N7:12 at the next
available position, 9
in this case.
N7:45
33
Loading and Unloading of Stack #N7:12
FFL and FFU Instruction Pair
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