Rockwell Automation 1785-Lx0C15 ControlNet PLC-5 Programmable Controllers User Manual - Manual (Page 47)

1785-UM022C-EN-P - February 2008
Planning to Use Your ControlNet PLC-5 Processor 2-9
Table 2.C ControlNet Immediate Data-Transfer Operations
Using Process Control Sample Complete
Scheduled data transfers occur continuously and asynchronously to
the program scan. If a scheduled connection is an input, then
incoming data is copied to a private input buffer upon its receipt.
If a scheduled connection is an output, then data from a private output
buffer is transmitted during each scheduled communication.
Your data table files and private buffers are synchronized during
housekeeping, which occurs between program scans. During
housekeeping, the latest inputs are copied from the private memory
buffers to the processor’s input data table files (file 1 and the DIF)
and the output data table files (file 0 and the DOF) are copied to the
private output buffers.
In some instances, however, it is useful to have access to new input
data as soon as it has been received without waiting for housekeeping
to take place at the end of the program scan. Process control sample
complete enables you to do so for the following scheduled connection
types:
• 1747 analog or module connection
• 1771 analog or module connection
• 1794 analog or module connection
• receive scheduled message
Instructions Description
In the case of an IIN, the most recent copy of the specified input word secured in the last discrete I/O
data transfer from the corresponding I/O chassis is used. This value is moved from the private
memory buffer to the working data table and is used in all subsequent ladder instructions. This data
could be as old as the time taken since the last asynchronous I/O update, and it may not actually
reflect the latest state of the input word.
In the case of an IOT, the current state of the specified output word is copied to the private memory
buffer and is used on the next output update to the I/O chassis. The actual change is not
communicated until the next asynchronous I/O transfer.
Only 1 word of I/O data can be updated per instruction.
The ControlNet Immediate Data I/O instructions work in much the same way as the immediate I/O
instructions. During an input instruction, the most recent data is copied from the private memory
buffer to a data-table address that you specify. In the case of an output instruction, the data is
copied from an area that you specify to the private memory buffer and sent on the next I/O update.
As many as 64 words can be transferred per instruction.
Important: In most cases, you should set the Data file offset and the Source of an IDO or the Data
file offset and the Destination of an IDI to the same address. See Chapter 4 for more information on
this and other aspects of using ControlNet IDI and IDO instructions.
Immediate I/O-ControlNet and Remote I/O
001
( ) IIN
001
( ) IOT
ControlNet Immediate Data I/O
IDI
IMMEDIATE DATA INPUT
Data file offset
Length
232
10
Destination N11:232
IDO
IMMEDIATE DATA OUTPUT
Data file offset
Length
175
24
Source N12:175