User guide

Instructions
Chapter 18
I/O Message and Communication
18–19
SLC 5/02 Processors Only
I/O Refresh REF Output Instruction
(REF)
(REF)
F1 F2 F3 F4 F5
ZOOM on REF –(REF)– 2.0.0.0.1
NAME: REFRESH I/O
EDT_DAT
HHT Ladder Display:
HHT Zoom Display:
Ladder Diagrams and APS Displays:
(monitor mode)
The REF instruction has no programming parameters. When it is evaluated
as true, the program scan is interrupted to execute the I/O scan, which
includes the service communications portion of the operating cycle (write
outputs, service comms, read inputs). The scan then resumes in the program
scan at the instruction following the REF instruction.
You are not allowed to place an REF instruction in an STI interrupt, I/O
interrupt, or user fault subroutine.
ATTENTION: The watchdog and scan timers are reset when
executing the REF instruction. You must insure that an REF
instruction is not placed inside of a non-terminating program
loop.
Do not place an REF instruction inside of a program loop
unless the program is thoroughly analyzed.
!
I/O Refresh (REF)