Rockwell Automation 6008-SV2R VMEbus remote I/O Scanner - Manual (Page 44)

Chapter
Communicating with Remote I/O
4
4Ć7
Important: The remote I/O scan for one channel is independent of and
asynchronous to the remote I/O scan for the other channel.
The status of the discrete devices is represented by a single bit in an input
or output group (word). The scanner is related to these devices as shown
in Figure 4.4.
Figure 4.4
The Relationship between the scanner and I/O
motor starter
PLCĆ5
15383
Up to 13 more
I/O adapters
remote
I/O link
operator
interface
terminal
VME
master
processor
scanner
VMEbus
backplane
VMEbus Subrack
processor
1771 I/O
chassis
input
modules
output
modules
pushbutton switch
1771
I/O
adapter
1771 I/O
chassis
input
modules
output
modules
channel
in adapter
mode
An external device, such as the switch shown above, causes an input of a
discrete input module to turn on. This sets a bit to a “1” condition in the
I/O module. The next time the I/O adapter scans the module, the new
information is reported to the adapter. When the scanner scans the adapter,
the corresponding bit in the I/O image table is set to a condition that
reflects the status of the external device, the switch.