B&B Electronics VFG3000 - Manual - Manual (Page 160)

P ROGRAM P ROPERTIES V LINX F IELDBUS G ATEWAY M ANAGER U SER M ANUAL
P AGE 144
to the approximate position of the error. If no errors exist, a dialog box will be displayed to
confirm this fact, and the program will be translated into Fieldbus Gateway Manager’s
internal format for subsequent execution by the Fieldbus Gateway.
P
ROGRAM
P
ROPERTIES
The various fields at the bottom of the right-hand pane are used to edit program properties…
• The Return Type property is used to indicate whether this program should simply
perform a series of actions, or whether it will perform a calculation and return
the value of that calculation to the user. Programs that return values are
described in more detail below.
• The Run In Background property is used to indicate whether Fieldbus Gateway
Manager should wait for the program to complete execution before continuing
with processing whatever task invoked the program. For example, if this
property is set to No, running a program in response to a key being pressed will
result in a pause in display updates until the program completes. (Since most
programs take very little time to execute, this may not even be noticeable.) If this
property is set to Yes, display updates will continue immediately, and the
program will execute at a lower priority in the background. Only one
background program will run at once, so subsequent requests are queued for later
execution. Note also that programs that return values cannot be run in the
background, as their return value would then not be available for the caller to
use!
• The External Data and Timeout properties are used to control how the program
interacts with Fieldbus Gateway Manager’s communication infrastructure with
respect to external data items to which the program makes reference. You will
recall that Fieldbus Gateway Manager only reads data items when they are used.
This property is used to control the exact interpretation of this rule with respect
to programs…
M
ODE
B
EHAVIOR
Read When Referenced External data used by the program will be added to the
comms scan whenever the program is referenced. If the
program is referenced by a display page, the data will be
read when that page is displayed; if the program is
referenced by a global action or a trigger, the data will be
read at all times. This is the default mode, and is
acceptable for all programs, except those that use very
large amounts of external data.
Read Always External data used by the program will be read at all
times, whether or not the program is referenced. This
means that the program will always be ready to run, and
that the operator will not see the “NOT READY” message
that might otherwise occur when the program is first
referenced. The downside of this mode is that comms
performance may be reduced if large amounts of data are