Rockwell Automation 1747-ASB Remote I/O Adapter - Manual (Page 19)

Publication 1747-UM006B-EN-P - June 2003
Overview 1-5
Creating More Than One Logical Device by Crossing a Logical
Rack Boundary
RIO discrete transfers occur on a logical device basis, not an adapter
basis. A logical device is any portion of a logical rack that is assigned
to a single adapter.
When an adapter's image is more than one logical device, the scanner
sees the single adapter as multiple adapters on the RIO link. The
scanner communicates with each logical device independently, even if
the logical devices are all assigned to one adapter. If an adapter
image is more than one logical device, the following is true:
Not all of the adapter image is updated by the scanner 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.
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
Bit Number (Octal) 0 7 17 10 Bit Number (Octal) 0 7 17 10
Adapter
Image
Adapter
Image
IMPORTANT
Due to SLC and PLC addressing differences, when
the 1747-ASB module is used with an SLC processor,
the image bit numbers are 0 to 7, 8 to 15 decimal.
When the 1747-ASB module is used with a PLC
processor, the image bit numbers are 0 to 7, 10 to 17
octal. The I/O image figures, like the two above,
indicate the type of image bit numbers used (octal,
decimal, or both) throughout this manual.