B&B Electronics VFG3000 - Manual - Manual (Page 199)

W RITING A CTIONS C HANGING P AGE
R EVISION 1 P AGE 183
W
RITING
A
CTIONS
While expressions are used to define values, actions are used to define what you want to
happen when a trigger or other event occurs. Since the vast majority of the actions in a
database will relate to key-presses, and since Fieldbus Gateway Manager provides a simple
method of defining commonly-used actions via the dialog box discussed in the User Interface
section, you will often be able to avoid writing actions “by hand”. Actions are needed,
though, if you want to use triggers, write programs, or use a key in User Defined mode.
C
HANGING
P
AGE
To create an action that changes the page shown on the Gateway’s display, use the syntax
GotoPage(Name) , where Name is the name of the display page in question. The current page
will be removed, and the new page will be displayed in its place.
C
HANGING
N
UMERIC
V
ALUES
Fieldbus Gateway Manager provides several ways of changing data values.
S IMPLE A SSIGNMENT
To create an action that assigns a new value to a tag or to a register in a communications
device, use the syntax
Data:=Value , where Data is the data item to be changed, and Value
is the value to be assigned. Note that Value need not just be a constant value, but can be any
valid expression of the correct type. Refer to the previous section for details of how to write
expressions. For example, code such as
[N7:0]:=Tank1+Tank2 can be used to add two tank
levels and store the total quantity directly in a PLC register.
C
OMPOUND
A
SSIGNMENT
To create an action that sets a data value equal to its current value combined with another
value by means of any of the operators defined in the previous section, use the syntax
Dataop=Value , where Data is the tag to be changed, Value is the value to be used by the
operator, and op is any of the available operators. For example, the code Tag+=10 will
increase Tag by a value of 10, while Tag*=10 will multiply the current value by 10.
I NCREMENT AND D ECREMENT
To create an action that increases a data value by one, use the syntax Data++ . To create an
action that decreases a tag by one, use the syntax Data-- . Note that the ++ or -- operators
may be placed before or after the data value in question. In the former case, the value of the
expression represented by
++Data is equal to the value of Data after it has been incremented.
In the latter case, the expression is equal to the value before it has changed.
C
HANGING
B
IT
V
ALUES
To change a bit within a tag, use the syntax Data.Bit:=1 or Data.Bit:=0 to set or clear the
bit as required, where Data is the tag in question and Bit is the zero-based bit number. Note
again that the value on the right-hand side of the := operator can be an expression if desired,