Rockwell Automation 1785-Lx0C15 ControlNet PLC-5 Programmable Controllers User Manual - Manual (Page 41)

1785-UM022C-EN-P - February 2008
Planning to Use Your ControlNet PLC-5 Processor 2-3
The frequency of I/O chassis backplane updates depends on the
adapter, the type of scheduled data transfer (rack or module
connection) and the number of different modules being updated.
Actual I/O throughput times must be determined with real products to
determine if the I/O throughput times meet the requirements of the
application.
Input data from the private memory buffer is put
into the input image file. New input data
may stay in the private memory buffer up to 1
program scan or until the next housekeeping. Scheduled data transfer
occurs between the PLC-5
and the adapter module in
the I/O chassis. Data may
stay in the private memory
buffer for up to 1 API.
In the same manner,
the I/O adapter has
scheduled I/O data
transfer with I/O
modules
Input data is written from the I/O module
to a private memory buffer on the adapter.
The new input data may stay in
the private memory buffer for as long
as it takes to complete the I/O chassis
backplane update.
In scheduled I/O data
transfer, updates occur
between logic scans
(i.e. during
"housekeeping")
Logic Scan
Housekeeping
Data
Table
Files Private
Memory
Buffers Private
Memory
Buffers
Scheduled Data
Transfer
Data Update
PLC-5 Programmable Controller
Adapter Module I/O Modules
Program Scan
Data Update
I/O Chassis
1 2 3
What Happens During Scheduled Input Data Transfer