Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 100)

Publication 1785-UM024B-EN-P - January 2003
C-2 Data Table Crossloading
An On-Demand data table crossload transfers data table data from the
primary processor to the secondary processor. To set up On-Demand
data table crossload operations, you must load configuration
information, identifying the files to be crossloaded. Then, to trigger an
On-Demand data table crossload, you must enter a non-zero value
into word 33 of the ControlNet Hot Backup Integer file. Functionally,
an On-Demand data table crossload is equivalent to a series of
Message Instructions; however, no ladder programming is required.
In addition to the crossloading mentioned above, there is Automatic
data table crossloading, occurring at the time of qualification, which
transfers data table values from the primary processor to
corresponding data table locations on the secondary processor.
This ensures that when a secondary processor becomes qualified, that
processor is immediately ready to take over control of the outputs
should a switchover occur.
If configured to crossload over the ControlNet channel, both the
On-Demand data table crossload and Qualification data table
crossload use the unscheduled bandwidth of the ControlNet channel.
You can also perform data table crossloads in ladder logic, via the
message instruction. When you perform data table crossloads via the
message instruction, you can use any available channel; you are not
limited to the ControlNet channel or channel 1A.
The data table crossload can be configured to occur over the
unscheduled bandwidth of the ControlNet channel or over DH+
(channel 1A). You may want to perform data table crossloads over
channel 1A when there is insufficient unscheduled bandwidth over
the ControlNet channel or bumps in activity on the unscheduled
bandwidth are undesired.
Also, data table crossloading only crossloads data table data (i.e., there
is no mechanism to crossload Program file information. It is up to you
to ensure that the proper program files are downloaded into your
processors.
IMPORTANT
Neither the On-Demand data table crossload nor the
Qualification data table crossload can occur unless
the data table structures are identical between the
two processors.