Allen-Bradley PLC-5 - Discrete Data Transfer

Publication 1785-UM012D-EN-P - July 2005
Communicating with Extended-Local I/O 8-5
Discrete Data Transfer
The time that it takes to scan extended-local I/O chassis is added to the
housekeeping time as shown in the following figure.
PLC-5/40L and -5/60L Extended-Local I/O Scan Time
AdapterAdapter Adapter
Housekeeping
Rack 3
Rack 2
Rack 1
Remote I/O
Buffer
Logic
Scan
Remote I/O
Scan
Program Scan
IOT (x)
IIN (y)
Immediate I/O
Processor-
Rack
Resident
I/O Image
Table
Data
Exchange
Update
I/O image
Extended
-local I/O
Data
Exchange
Data
Exchange
a
b
a
write outputs
b
read inputs
x
y
xy
Data exchange occurs during housekeeping. Outputs are written to
and inputs read from the I/O image table during the logic scan.
IIN and IOT data transfer directly to and
from I/O modules extended-local I/O chassis.
The processors scan the extended-local I/O chassis during the
housekeeping portion of the program scan. Extended-local I/O
discrete data is exchanged between the processor’s data table
image and the I/O in the extended-local I/O chassis.
1
1
+Processor
Checks
Remote
I/O Buffer
Update
Processor
Resident
I/O Update
Extended-
Local I/O
Scan
Housekeeping
Program Scan
Logic Scan