Rockwell Automation 1747-ASB Remote I/O Adapter - Manual (Page 20)

Publication 1747-UM006B-EN-P - June 2003
1-6 Overview
The adapter may receive different communication commands for each
logical device. In this case, the adapter decides which command it
responds to.
To understand how an adapter's logical devices are assigned, use
appendix D to determine the address configuration of your remote
I/O modules. You may then want to reassign certain adapters so their
images do not cross logical rack boundaries, allowing the scanner to
update their images in one RIO discrete transfer.
Transferring Data With RIO Discrete and Block Transfers
Input and output image data and command information is quickly
exchanged between a scanner and adapter using RIO discrete
transfers. RIO discrete transfers are the simplest way a scanner and
adapter communicate with each other. RIO discrete transfers, which
are transparent to the user, consist of the scanner sending the output
image data to the adapter, and the adapter transmitting input data to
the scanner. Each RIO discrete transfer also contains scanner
commands for the adapter.
Group 2
Group 3
Group 0
Group 1
Group 6
Group 4
Group 5
Group 7
Logical
Rack 1
Group 7
Group 5
Group 6
Group 3
Group 4
Group 1
Group 2
Group 0
Logical
Rack 0
Adapter
Image
Logical
Device
Logical
Device
Bit Number (Decimal) 0 7 8 15
Scanner Input or Output Image
Bit Number (Octal) 0 7 17 10
In this example, two RIO
discrete transfers are
required for the scanner to
update the adapter image
containing two logical
devices.
IMPORTANT
The 1747-ASB module always functions as one
adapter on the RIO link, even though it may contain
more than one logical device. For example, the
1747-ASB module does not begin normal operation
until all of its logical devices are receiving RIO
discrete transfers from the scanner.