Block Transfer Application Example; Scanner Configuration - Allen-Bradley 1747-SN User Manual

7–14 Application Examples
Block Transfer Application
Example
Publication 1747 6.6 - July 1996
In the following example, a technician has these requirements:
install a 4 to 20 mA transducer located approximately 701 meters
(2,300 feet) from an SLC 5/03 processor
bring this analog input value from the transducer into the SLC
processor as well as display the analog value on a meter at the
remote location
the meter must display 0 to 100% and accept a 4 to 20 mA signal
in addition, the remote I/O scanner in the SLC processor chassis
has only 1/4 logical rack of I/O image space remaining (due to
other RIO devices on this RIO link)
needs 16 discrete inputs and 16 discrete outputs at this same
remote location
The local system consists of (refer to system layout diagram):
a Catalog Number 1747-L532 processor (SLC 5/03) in slot 0
a Catalog Number 1747-SN scanner (RIO Scanner) in slot 1 with
only 1/4 logical rack of the I/O image available
With only 1/4 logical rack image to work with, the remote system
consists of (refer to system layout diagram):
4-slot remote chassis with a 1747-ASB in slot 0
1746-IV16 module in slot 1
1746-OV16 module in slot 2
1746-NIO4I in slot 3
2-slot addressing must be selected for the remote chassis to keep its
image size to 1/4 logical rack. The discrete modules use the entire
image for logical rack 3, group 6 in a complementary slot pair
arrangement and the combination analog module uses the image for
logical rack 3, group 7. This image size for the analog module is 1
input and 1 output word short of what is required by the NIO4I
module. Therefore, block transfer to/from the analog module will be
used (BT operations only require one input and one output byte). In
the future, the other analog input and output on the 1747-NIO4I may
be used.

Scanner Configuration

The technician addresses the 1747-ASB to logical rack 3, starting
logical group 6. Since the analog module's image (2 input/output
words) will not fit into one logical group (1 input/output word), he
must use block transfer to read analog input values and write to
analog outputs. In this example, the SLC processor will receive the
analog input data via BTR, scale it, and send it to the analog output
via a BTW.