Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 106)

Publication 1785-UM024B-EN-P - January 2003
C-8 Data Table Crossloading
The Qualification State data table crossload is almost identical to the
On-Demand data table crossload discussed previously. The only
differences are:
• the Qualification State data table crossload occurs automatically
during qualification whereas you must trigger the On-Demand
data table crossload
• the Qualification State data table crossload always performs all
four crossload operations (Timer Accumulators, Counter
Accumulators, PD files, and User Selectable files), whereas the
On-Demand data table crossload allows you to select which
combination of the four operations get performed
Data Table Crossload Time
It may take many seconds for any of the above instances of data table
crossloading to finish. The time it takes to do the data table crossload
primarily depends on the amount of data table data to be crossloaded.
The data table crossload is performed using the unscheduled
bandwidth of the ControlNet channel. The amount of available
unscheduled bandwidth on the ControlNet channel also influences the
amount of time needed to perform the data table crossload.
Additionally, if Data Highway Plus crossloading is selected, the times
will differ.
There are two words which indicate how long it takes the data table
crossload to finish: one for the Qualification data table crossload
(word 50 in the ControlNet Backup Integer File), and one for the most
recent occurrence of either the On-Demand data table crossload or
the Qualification State data table crossload (word 51 in the ControlNet
Backup Integer File). The time units are in seconds.
Data Table Crossload Data Latency
Even though a data table crossload may take many seconds to
complete, the data that is transferred from the primary processor to
the qualifying or secondary processor is fresh. In other words, the
crossloaded data is not sitting in a buffer getting stale waiting for all
the data to be crossloaded. Each packet of data is immediately written
into the other processor’s data table. So, no matter how long the data
table crossload takes, the data table elements which are crossloaded
into the qualifying or secondary processor closely match the values in
the primary processor.