Rockwell Automation 8520-9API 9/Series OCI API Developer's Guide - Manual (Page 97)

4–49 OCI Data Server Data Items
Publication 8520-6.6 - August 1999
$ System Flags
Data Type
Defined by PAL
Read/Write Read/Write (PAL protected)
Array Index none
Control Type Lathe/Mill/Grinder 1
1 Grinder Control Type is not available for Release 1 of 9/PC.
You can access all PAL/Logic system flags provided they are
available on your 9/Series executive type (e.g. some grinder system
flags are not available on a lathe/mill). All read and writes are
subject to the logic which always has the authority to override any
OCI settings.
Automatic reads of PAL/Logic variables are always added to the
controls background watch list. You must consider any timing issues
this may present in your PAL/Logic and API applications.
Variables set by the OCI occur at the beginning of a PAL scan. The
PAL/Logic ladder runs and acts on these changes by writing to the
variable tables. This means if your OCI sets an output to true at the
beginning of a PAL/Logic scan, PAL/Logic can change the output
point back to false during the PAL/Logic scan thus overriding the
OCI request to set the output to true.
PAL/Logic system variables that are defined by PAL/Logic as
foreground only are also added to the OCI Foreground watchlist.
Foreground/Background selectable and Background only PAL/Logic
system variables are always loaded in to the OCI background
watchlist as most other OCI API data items.
Format for this data item is $ followed by the name of the system
variable:
$ESTOPI
Important: For the 9/PC, flags have a different syntax in Logic.
API still uses the “$” format.
There can be timing issues related to variables that are altered
through the logic, for example if your OCI station changes a
PAL/Logic variable that is later changed in the foreground scan the
last device (PAL/Logic or the OCI station) that changes the data will
be used. The foreground/background state of an OCI PAL/Logic
system variable is defined in your PAL/Logic reference manual and
not set by simply writing the variable in a foreground or background
PAL/Logic module.