Installation manual

Publication 1747-RM001G-EN-P - November 2008
6-10 Program Flow Instructions
I/O Refresh (REF)
Using an SLC 5/02 Processor
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 (write outputs, service comms,
read inputs). The scan then resumes at the instruction following the REF
instruction.
You are not allowed to place a REF instruction in an STI subroutine, I/O
subroutine, or user fault subroutine.
Using SLC 5/03 and Higher Processors
Operation of the REF instruction in the SLC 5/03 and higher processors is
the same as the SLC 5/02 processor. However, when using the SLC 5/03 and
higher processors, you can also select a specific communication channel to be
serviced.
• SLC 5/03 processor.
– channel 0 is RS-232/DF1 Full-duplex, DF1 Half-duplex (master or
slave), DF1 Radio Modem, DH-485, or ASCII
– channel 1 is DH-485
• SLC 5/04 processor.
– channel 0 is RS-232/DF1 Full-duplex, DF1 Half-duplex (master or
slave), DF1 Radio Modem, DH-485, or ASCII
– channel 1 is DH+
• SLC 5/05 processor.
– channel 0 is RS-232/DF1 Full-duplex, DF1 Half-duplex (master or
slave), DF1 Radio Modem, DH-485, or ASCII
– channel 1 is Ethernet
You are not allowed to place a REF instruction in a DII subroutine, STI
subroutine, I/O subroutine, or user fault subroutine.
(REF)
SLC 5/02 Processor
Output Instruction
Fixed SLC
5/01
SLC
5/02
SLC
5/03
SLC
5/04
SLC
5/05
••••
ATTENTION
The watchdog and scan timers are reset when
executing the REF instruction. You must insure that
an REF instruction is not placed inside a
non-terminating program loop. Do not place an REF
instruction inside a program loop unless the program
is thoroughly analyzed.
REF
Refresh I/O
Channel 0 Yes
Channel 1 No
REF