Rockwell Automation 1747-SCNR ControlNet Scanner Module Reference Manual - Manual (Page 23)

Publication 1747-RM623D-EN-P - June 2006
Prepare to Use the ControlNet Scanner 2-3
Understand ControlNet
Data transfer The ControlNet system is designed to do this:
• Provide high-speed, repeatable, deterministic I/O transmission.
• Let control and message information co-exist on the same
physical media.
• Make sure that I/O data transfers are not affected by:
• programming-terminal activity.
• inter-scanner message activity on the network.
Scheduled Data Transfer Operations on a ControlNet Network
ControlNet scheduled data transfer on a 1747-SCNR Scanner:
• is continuous.
• transmits on the network asynchronously to the ladder logic
program scan.
• occurs at the actual rate that is determined by RSNetWorx for
ControlNet software.
For discrete I/O data transfer between logic scans (during
housekeeping), the following updates occur.
• The gathered input image is moved from the scanner to the SLC
processor's input image file for use during the next logic scan.
• The 1747-SCNR output data is updated with data from the SLC
processor output image file and is sent during the next
scheduled communication.
M0 and M1 files are data files that reside in the 1747-SCNR scanner
only. Data from these files will be available to the SLC processor using
ladder instructions. Scheduled data update will be triggered by the
Housekeeping period start, which occurs once per scan. This process
is illustrated below.
Data
Table
Files
Lo
gi
c S
ca
n
Scheduled
Data
Private
Memory
Buffers
Sc
he
dule
d Da
ta
Tr
an
sf
er
s
Housekeeping
41554
SLC 500 Program Scan Data Tables Files Housekeeping
Data Update
1747-SCNR Scheduled Data