Allen-Bradley 1747-SN - SLC and Scanner Asynchronous Operation

1–5Overview
Publication 17476.6 - July 1996
SLC and Scanner Asynchronous Operation
The SLC processor scan and RIO scanner scan are independent
(asynchronous) of each other. The SLC processor reads the scanner
input image file during its input scan and writes the output image file
to the scanner during its output scan. The RIO scanner continues
reading inputs and writing outputs to the scanner I/O image file,
independent of the SLC processor scan cycle.
Depending on your SLC processor, RIO link configuration, and
application program size, the scanner may complete multiple scans
before the SLC processor reads the scanner’s input image file. The
RIO scanner updates its I/O files on a per logical rack basis.
The figure below illustrates the asynchronous operation of the SLC
processor and RIO scanner.
SLC Processor
SLC Processor Scan Cycle RIO Scanner Scan Cycle
Program
The scanner updates its
input image file each time
it scans a logical device.
The scanner may scan all
of its configured logical
devices several times
before the SLC processor
reads the scanner's input
image file.
The SLC processor reads the
scanner input image file into the
SLC input image file, processes
it, and creates an SLC output
image file. The SLC processor
transfers its output file to the
scanner.
SLC Input
Image File
SLC Output
Image File
Scanner
Input
Image File
Scanner Output
Image File
Output
Image
Device 3
Output
Image
Device 2
Output
Image
Device 1
Input
Image
Device 3
Input
Image
Device 2
Input
Image
Device 1
Important: The outputs of the RIO are updated after the end of the first SLC processor scan.