Allen-Bradley MicroLogix 1000 User Manual

Using Data Handling Instructions
9–25
FIFO Load (FFL) and FIFO Unload (FFU)
FFL and FFU instructions are used in pairs. The FFL instruction loads words into a
user-created file called a FIFO stack. The FFU instruction unloads words from the
FIFO stack in the same order as they were entered.
Operation
Instruction parameters have been programmed in the FFL – FFU instruction pair
shown below .
(EM)
(EN)
(DN)
(EM)
FFL
FIFO LOAD
Source N7:10
FIFO #N7:12
Control R6:0
Length 34
Position 9
(EU)
FFU
FIFO UNLOAD
FIFO #N7:12
Dest N7:11
Control R6:0
Length 34
Position 9
FFU instruction unloads data
from stack #N7:12 at position 0,
N7:12.
N7:12
0
N7:13
1
N7:14
2
3
4
5
6
7
8
9
33
34 words are allocated
for FIFO stack starting at
N7:12, ending at N7:45.
FFL–FFU Instruction Pair
Loading and Unloading of Stack #N7:12
N7:10
N7:11
PositionDestination
Source
FFL instruction loads data into
stack #N7:12 at the next available
position, 9 in this case.
N7:45
(DN)
FFL Instruction
When rung conditions change from false-to-true, the controller sets the FFL enable
bit (EN). This loads the contents of the Source, N7:10, into the stack structure
indicated by the Position number, 9. The position value then increments.
The FFL instruction loads an element at each false-to-true transition of the rung,
until the stack is filled (34 elements). The controller then sets the done bit (DN),
inhibiting further loading.
Programming
Execution Times
(µsec) when:
True False
61.13 33.67
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Allen-Bradley MicroLogix 1000 Specifications

General

Brand	Allen-Bradley
Model	MicroLogix 1000
Category	Controller
Language	English