Rockwell Automation 1785-Lx0C15 ControlNet PLC-5 Programmable Controllers User Manual User Manual

Page 40

1785-UM022C-EN-P - February 2008

2-2

Planning to Use Your ControlNet PLC-5 Processor

Scheduled Data-Transfer Operations on a ControlNet Network

ControlNet scheduled data transfer on a ControlNet PLC-5 processor:

•

is continuous

•

is asynchronous to the ladder-logic program scan

•

occurs at the actual rate displayed in the Actual Packet Interval
(API) field on the programming software scanlist configuration
screen in RSNetWorx for ControlNet software

Important: The Requested Packet Interval (RPI) rate requested for a
connection establishes the data transfer rate on the ControlNet
network. API is determined by RSNetWorx software when the
schedule is built. The API will always be the same or less than the
RPI.

The API does not imply the actual I/O throughput. I/O data is sent on
the network every API regardless of whether the I/O data has been
refreshed with newer I/O data. I/O throughput time may be slower
due to delays caused by module update times, processor scan times
and adapter to I/O module transfer times.

Data from the output-image file is put into
a private memory buffer. New output data
may stay in the data table files 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

Output data is written from a private
memory buffer on the adapter to the
module. The output data stays in
the private memory buffer for as long
as it takes the I/O chassis backplane
update to occur.

In scheduled I/O data
transfer, updates occur
between logic scans
(i.e. during
"housekeeping")

Logic Scan

Housekeeping

Data
Table
Files

Private
Memory
Buffers

Scheduled Data
Transfer

Data Update

PLC-5 Programmable Controller

Adapter Module

I/O Modules

Program Scan

Data Update

I/O Chassis

What Happens During Scheduled Output Data Transfer