Allen-Bradley SLC 500 Series User Manual

Publication 1747-RM001G-EN-P - November 2008
Data Handling Instructions 5-29
LFL Instruction Operation
When rung conditions change from false-to-true, the LFL enable bit (EN) is
set. This loads the contents of the source, N7:10, 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 processor then sets the done
bit (DN), inhibiting further loading.
LFU Instruction Operation
When rung conditions change from false-to-true, the LFU enable bit (EU) is
set. This unloads data from the last element loaded into the stack (at the
position value minus 1), placing it in the destination, N7:11. 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 processor then sets the empty bit (EM).

Allen-Bradley SLC 500 Series Specifications

General

Programming Software	RSLogix 500
Series	SLC 500
Category	Controller
Manufacturer	Allen-Bradley (Rockwell Automation)
I/O Capacity	Up to 4096 I/O points
Communication Ports	DH-485
Programming Languages	Ladder Logic
Operating Temperature	0 to 60 °C (32 to 140 °F)
Relative Humidity	5% to 95% (non-condensing)
Memory	4K to 64K words (depending on the processor)
Power Supply	AC or DC (depending on the module)