Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 213)

Chapter 11
Using Data Handling Instructions
11–30
P 0 0 0 L F L S R C
N 1 0 0
P 0 0 0 L F L L I F O
# N 1 2 0
P 0 0 0 L F L R 0 0
L 3 4 P 9
P 0 0 0 L F U L I F O
# N 1 2 0
P 0 0 0 L F U D E S T
N 1 1 0
P 0 0 0 L F U R 0 0
L 3 4 P 9
LFL Instruction
When rung conditions change from false-to-true, the controller sets the LFL
enable bit (EN). This loads the contents of the Source, N10, into the stack
element indicated by the position number, 9. The position value then
increments.
The LFL instruction loads an element at each false-to-true transition of the
rung, until the stack is filled (34 elements). The controller sets the done bit
(DN), inhibiting further loading.
LFU Instruction
When rung conditions change from false-to-true, the controller sets the LFU
enable bit (EU). This unloads data from the last element loaded into the
stack (at the position value minus 1), placing it in the Destination, N11. The
position value then decrements.
The LFU instruction unloads one element at each false-to-true transition of
the rung, until the stack is empty. The controller then sets the empty bit
(EM).
LFL instruction loads data
into stack #N12 at the next
available position, 9 in this
case.
LFU instruction unloads
data from stack #N12 at
position 8.
N12
0
N13
1
N14
2
3
4
5
6
7
8
9
33
34 words are
allocated for LIFO
stack starting at
N12, ending at N45.
LFL–LFU Instruction Pair Loading and Unloading of Stack #N12
N10
N11
Position Destination
Source
N45
N15
N16
N17
N18
N19
N20
N21