Publication 1762-RM001C-EN-P
17-4 Input and Output Instructions
Addressing Modes and File Types can be used as shown below:
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
push-button, DAT [MicroLogix 1500 only], 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.
Table 17.4 IOM Instruction Valid Addressing Modes and File Types
For definitions of the terms used in this table see Using the Instruction Descriptions on page4-2.
Parameter
Data Files Function Files
CS - Comms
IOS - I/O
Address
Mode
Address
Level
O
I
S
B
T, C, R
N
ST
L
MG, PD
RTC
HSC
PTO, PWM
STI
EII
BHI
MMI
DAT
TPI
Immediate
Direct
Indirect
Bit
Word
Long Word
Element
Slot • • •
Mask •• •••
• • ••
Length
•
REF
Table 17.5 Execution Time for the REF Instruction
Controller When Rung Is:
True False
MicroLogix 1200 see p. A-7 0.0
µ
s
MicroLogix 1500 see p. B-6 0.0
µ
s
NOTE
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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