Rockwell Automation 1747-ASB Remote I/O Adapter - Manual (Page 21)

Publication 1747-UM006B-EN-P - June 2003
Overview 1-7
RIO block transfers are initiated by a special command from the PLC
processor, typically when large amounts of data must be exchanged
with one specialty I/O module. Block transfers use the basic RIO
discrete transfer mechanism of the RIO link. However, the actual
transfer of data occurs asynchronous to the discrete transfers. It is
possible for several discrete transfers to occur before a block transfer
is processed.
RIO Discrete Transfer Example
This example illustrates how additional discrete transfers are required
when an adapter image crosses logical rack boundaries. It consists of
one scanner and three adapters. Adapter 1 requires one RIO discrete
transfer from the scanner to update its entire image. Adapter 2
requires two RIO discrete transfers to update its image. Adapter 3
requires three RIO discrete transfers to update its image.
(1) The scanner updates the adapter image in one RIO discrete transfer because the adapter image is contained
within one logical rack.
(2) The scanner updates the adapter image in two RIO discrete transfers because the adapter image crosses a
logical rack boundary making the adapter image appear as two logical devices.
(3) The scanner updates the adapter image in three RIO discrete transfers because the adapter image crosses two
logical rack boundaries making the adapter image appear as three logical devices.
Adapter 2 Configured As:
Starting Logical Rack: 0
Starting Logical Group: 6
Adapter Image Size: 8 logical groups
Adapter 1 Configured As:
Starting Logical Rack: 0
Starting Logical Group: 0
Adapter Image Size: 6 logical groups
Adapter 3 Configured As:
Starting Logical Rack: 1
Starting Logical Group: 6
Adapter Image Size: 18 logical groups
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
Logical
Rack 2
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
Logical
Rack 3
Adapter 2
Logical Device 1
Adapter 1
Logical Device 1
Adapter 2
Logical Device 2
Adapter 3
Logical Device 1
Adapter 3
Logical Device 2
to scanner
Adapter 3
Logical Device 3
(3)
(2)
(1)
Bit Number (Decimal) 0 7 8 15
Scanner Input or Output Image
Bit Number (Octal) 0 7 17 10
1747-ASB Module