Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 75)

Publication 1747-UM010B-EN-P - September 2003
Configuration and Programming 5-13
Creating More than One Logical Rack Device
RIO discrete transfers occur on a logical device basis, not on an
adapter basis. A logical device is any portion of a logical rack that is
assigned to a single adapter.
When the scanner image assigned to an adapter is more than one
logical device, the scanner sees the single physical device as multiple
logical devices on the RIO link. The scanner communicates with each
logical device independently, even if the logical devices are all
assigned to one adapter. If a physical device image is more than one
logical device, the following is true:
•
The scanner does not update all of the adapter image at the
same time. The number of logical devices determines the
number of RIO discrete transfers that are needed to update the
entire adapter image.
•
The adapter may receive different communication commands for
each logical device. In this case, the adapter decides which
command it responds to.
0 7 8 15
In this example, the adapter is
configured to start at Logical Rack 0,
Logical Group 0, and uses 14 words
of I/O image. Note that two RIO
discrete transfers are required for the
scanner to update the adapter image
containing two logical devices.
Logical
Rack 0
Logical
Rack 1
Adapter
Image
Group 0
Group 1
Group 2
Group 3
Group 4
Group 5
Group 7
Group 0
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Group 7
Group 6
Logical
Device
Logical
Device