Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 75)

Publication 1785-UM012D-EN-P - July 2005
Communicating with Remote I/O 6-3
Introduction to Remote I/O A remote I/O system lets you control I/O that is not within the controller’s
chassis. A PLC-5 controller channel, in scanner mode, transfers discrete and
block-transfer data with remote I/O devices.
An example remote I/O system looks like this:
The remote I/O scanner channel keeps a list of all of the devices connected to
each remote I/O link called a scan list. An example channel scan list looks like
this:
Remote I/O link cable: Belden 9463
PLC-5/40
1771-ASB
PLC-5/20
A PLC-5 controller channel acting as a scanner
The scanner channel maintains a list of all the full and
partial racks connected to that channel, which is
the scan list.
Remote I/O node adapters like the 1771-ASB modules
or PanelView operator interfaces addressed
as remote I/O racks.
PLC-5 channel or a controller operating as
a remote I/O adapter
PLC-5/40E
Rack 1
Rack 2
Rack 3
Ch 1A
Ch 1B
Ch 1B Scan List
Rack
Addres
s
Starting
Group Rack
Size
Range
1
2
3 0
0
0 Full
1/2
Full 010-017
020-023
030-037
In this example, channel 1B continually scans the three racks in its scan list and
places the data in the remote I/O buffer in the controller. The controller updates
its own buffer and the I/O image table. During housekeeping, the two buffers are
updated by exchanging the input and output data with each other.
For more information on scan lists, see page 6-9.
.