Rockwell Automation 1747-ASB Remote I/O Adapter - Manual (Page 16)

Publication 1747-UM006B-EN-P - June 2003
1-2 Overview
To better understand the use of the 1747-ASB module, you should
have an understanding of the RIO link. The RIO link is an
Allen-Bradley communications system supporting high-speed transfer
of control information. An RIO link consists of a single master device
and one or more slave devices. The master device is referred to as the
scanner. The slave devices are referred to as adapters (such as the
1747-ASB module).
Remote I/O Overview RIO scanners and adapters work together to serially communicate PLC
or SLC processor data to remotely located I/O devices. PLC and SLC
processors exchange inputs and outputs with scanners. Scanners
exchange inputs and outputs with adapters located on the RIO link.
The adapter's control is based on the adapter type.
How The Scanner Interacts With Adapters
The scanner's function is to continuously scan the adapters on the RIO
link in a consecutive manner. The scan consists of one or more RIO
discrete transfers to each adapter on the RIO link.
RIO discrete transfers consist of the scanner sending output image
data and communication commands to the adapter that instruct the
adapter on how to control its output. (These include run, reset,
adapter reset, and reset decide commands.) The adapter responds by
sending input data to the scanner. The scanner performs as many RIO
discrete transfers as necessary to update the entire adapter image. If
RIO discrete transfers do not occur, data is not exchanged between
the scanner and adapter.
IMPORTANT
RIO discrete transfers are asynchronous with the
processor scan.