Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 71)

Publication 1785-UM012D-EN-P - July 2005
Communicating with Controller-Resident I/O 5-3
Transferring Data to
Controller-Resident I/O A PLC-5 controller transfers discrete and block-transfer data with
controller-resident I/O.
Transferring Discrete Data to Controller-Resident I/O
Transferring Immediate I/O Requests
The controller responds to immediate input (IIN) and immediate output
(IOT) requests during the logic scan. The logic scan is suspended at the
request for immediate input/output data. The logic scan resumes after
obtaining the data and fulfilling the request.
IIN data transfers directly to and IOT data transfers directly from I/O
modules in controller-resident I/O and extended-local I/O chassis. With
remote I/O, only the remote I/O buffer is updated. For more information, see
Appendix D.
The controller scans controller-resident local I/O
synchronously and sequentially to the program scan.
Controller-
Rack
Resident
I/O Image
Table
Data
Exchange
Housekeeping
Logic
Scan
Program Scan
Update
I/O image
a
write outputs
b
read inputs
a b
The controller-resident rack exchanges
discrete I/O information with the I/O image table
during housekeeping.
IOT (x)
IIN (y)
x
y
Immediate I/O
See explanation below.
TIP
When you place I/O modules, do not place a
block-transfer module next to or in the same module group
as an input module that you plan to use for immediate I/O.
Place the modules in non-adjacent slots. Placing input
modules for immediate I/O next to block-transfer modules
can result in a -5 Block-Transfer Read error.