Ffu - First In, First Out (Fifo) Unload - Allen-Bradley MicroLogix 1400 Instruction Manual

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FFU - First In, First Out
(FIFO) Unload
FFU FFU
EU
FIFO Unload
FIFO #N7:0
Dest N7:1 DN
Control R6:0
Length 1< EM
Position 0<
FFL
FIFO LOAD
Source
FIFO
Control
Length
Position
FFU
FIFO UNLOAD
FIFO
Dest
Control
Length
Position
FFL and FFU Instruction Pair
Instruction Type: output
Execution Time for the FFU Instruction
Controller Data Size
MicroLogix 1400 word
long word
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. Instruction parameters have been
programmed in the FFL - FFU instruction pair shown below.
(EN)
Destination
N7:10
(DN)
#N7:12
N7:11
(EM)
R6:0
34
9
FFU instruction
unloads data from
stack #N7:12 at
(EU)
#N7:12
(DN) position 0, N7:12
N7:11
(EM)
R6:0
34
9
Source
N7:10
FFL instruction loads
data into stack
#N7:12 at the next
available position, 9
in this case.
This instruction uses the following operands:
• FIFO - The FIFO operand is the starting address of the stack.
When Rung Is:
True
8.7180 µs
9.8890 µs
Position
N7:12 0
N7:13 1
N7:14 2
3
4
5
6
7
8
9
N7:45 33
Loading and Unloading of Stack #N7:12
Publication 1766-RM001A-EN-P - October 2008
File Instructions 279
False
6.6490 µs
7.2150 µs
34 words are allocated
for FIFO stack starting
at N7:12, ending at
N7:45