Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 19)

Publication 1747-UM010B-EN-P - September 2003
Overview 1-5
SLC and Scanner
Asynchronous Operation The SLC processor scan and Backup 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 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
backup scanner updates its I/O files on a per logical rack basis.
The figure below illustrates the asynchronous operation of the SLC
processor and backup scanner.
Backup Scanner Scan
The scanner updates its input
image file each time it scans a
logical device.
Scanner
Input
Image File Output
Device 3 Input
Device 1
Output
Device 1
Input
Device 2 Output
Device 2
Input
Device 3
Scanner Output Image File
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.
Backup Scanner Scan Cycle
Program
SLC Input
Image File
Scanner Input
Image File
Output Image
Device 3
Input Image Device 1
Output Image
Device 1
Input
Image
Device 2
Output Image
Device 2
Input Image
Device 3
SLC Output
Image file Scanner Output
Image File
SLC Processor
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 Processor Scan Cycle
IMPORTANT
The outputs of the RIO are updated after the end of
the first SLC processor scan.