Allen-Bradley MicroLogix 1100 Instruction Set Reference Manual

Publication 1763-RM001C-EN-P - October 2009
258 Input and Output Instructions
REF- I/O Refresh
Instruction Type: output
The REF instruction is used to interrupt the program scan to execute the
I/O scan and service communication portions of the operating cycle for
all communication channels. This includes: write outputs, service
communications (all communication channels, communications toggle
functionality, and comms housekeeping), and read inputs.
The REF instruction has no programming parameters. When it is evaluated
as true, the program scan is interrupted to execute the I/O scan and
service communication portions of the operating cycle. The scan then
resumes at the instruction following the REF instruction.
The REF instruction cannot be executed from an STI subroutine, HSC
subroutine, EII subroutine, or a user fault subroutine.
REF
Execution Time for the REF Instruction
Controller When Rung Is:
True False
MicroLogix 1100 see p. 462 0.84 μs
TIP
Using an REF instruction may result in input data
changing in the middle of a program scan. This
condition needs to be evaluated when using the REF
instruction.
ATTENTION
The watchdog and scan timers are reset when executing
the REF instruction. You must insure that the REF
instruction is not placed inside a non-terminating
program loop. Do not place the REF instruction inside a
program loop unless the program is thoroughly
analyzed.
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Allen-Bradley MicroLogix 1100 Specifications

General

Brand	Allen-Bradley
Model	MicroLogix 1100
Category	Controller
Language	English