Rockwell Automation 1747-SN Remote I/O Scanner - Manual (Page 57)

Publication 1747-UM013B-EN-P - January 2005
Scanner Configuration and Programming 4-13
• The address and size of the devices you list in the G file must
match the settings of each RIO device.
Crossing Logical Rack Boundaries
You express remote I/O image boundaries in an even number of
groups. For example, the 1747-ASB image can be any size from two
logical groups up to 32 logical groups (four logical racks), in 2 logical
group increments.
If the scanner image assigned to an adapter is greater than 8 logical
groups (one logical rack), the image crosses logical rack boundaries.
If the scanner image assigned to an adapter is less than 8 logical
groups, it too can cross a logical rack boundary depending upon the
starting logical group number. The significance of crossing logical rack
boundaries is discussed in the next section.
Examples of Crossing Logical Rack Boundaries
Examples 1 and 2 that follow show adapters with logical image sizes
that cross logical racks 0 and 1. The image size of the adapter in
example 1 consumes all of logical rack 0 (eight logical groups) and
half of logical rack 1 (four logical groups). The image size of the
adapter in example 2 consumes two groups in logical rack 0 and four
groups in logical rack 1.
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.
Bit Number (Decimal)
Logical
Rack 1
0 7 8 15
Scanner Input or Output Image
Logical
Rack 0
Group 2
Group 3
Group 0
Group 1
Group 6
Group 4
Group 5
Bit Number (Decimal)
Group 7
Logical
Rack 1
0 7 8 15
Scanner Input or Output Image
Group 7
Group 5
Group 6
Group 3
Group 4
Group 1
Group 2
Group 0
Logical
Rack 0
Adapter image is 12 logical groups in size and
crosses a logical rack boundary due to its size. Adapter image is 6 logical groups in size and crosses a logical
rack boundary due to its starting logical group number.
.
Group 2
Group 3
Group 0
Group 1
Group 6
Group 4
Group 5
Group 7
Group 7
Group 5
Group 6
Group 3
Group 4
Group 1
Group 2
Group 0
Adapter
Image
Adapter
Image
Crossing Logical Rack Boundaries - Example 1 Crossing Logical Rack Boundaries - Example 2