Allen-Bradley micrologix 1500 - LFU - Last In, First out (LIFO) Unload

Publication 1762-RM001C-EN-P
File Instructions 14-17
LFU - Last In, First Out
(LIFO) Unload
Instruction Type: output
On a false-to-true rung transition, the LFU instruction unloads words or
long words from a user-created file called a LIFO stack. The data is
unloaded using last-in, first-out order. Instruction parameters have been
programmed in the LFL - LFU instruction pair shown below.
EU
DN
EM
LFU
LIFO Unload
LIFO #N7:0
Dest N7:1
Control R6:0
Length 1<
Position 0<
LFU
Table 14.16 Execution Time for the LFU Instruction
Controller Data Size When Rung Is:
True False
MicroLogix 1200 word 29.1
µ
s10.4
µ
s
long word 31.6
µ
s10.4
µ
s
MicroLogix 1500 word 25.6
µ
s9.7
µ
s
long word 27.4
µ
s9.7
µ
s
(DN)
(EN)
(DN)
(EM)
LFL
LIFO LOAD
Source N7:10
LIFO #N7:12
Control R6:0
Length 34
Position 9
(EU)
(EM)
LIFO UNLOAD
LIFO #N7:12
Dest N7:11
Control R6:0
Length 34
Position 9
LFU
Destination Position
N7:11 N7:12 0
N7:13 1
LFU 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
LFL 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
LFL and LFU Instruction Pair