Rockwell Automation 1747-SN Remote I/O Scanner - Manual (Page 13)

Publication 1747-UM013B-EN-P - January 2005
Overview 1-5
The figure below illustrates the asynchronous operation of the SLC
processor and RIO scanner.
How the Scanner Interacts
with Adapters The scanner’s function is to continuously scan the adapters on the RIO
link in a consecutive manner. This scan consists of one or more RIO
discrete transfers to each adapter on the RIO link.
RIO discrete transfers consist of the scanner sending output image
data and communication commands to the adapter that instruct the
adapter on how to control its output. (These include run, adapter
reset, and reset decide commands.) The adapter responds by sending
input data to the scanner. The scanner performs as many RIO discrete
transfers as necessary to update the entire adapter image. If RIO
discrete transfers do not occur, data is not exchanged between the
scanner and adapter. RIO discrete transfers are asynchronous to the
processor scan.
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.