ProSoft Technology ProSoft i-View - Manual (Page 30)

Data Source Files ProSoft i-View ♦ Mobile Process Monitoring and Control Application
User Manual Version 2.0.2
Page 30 of 106 ProSoft Technology, Inc.
September 29, 2011
value expression Specifies a value to write on the related tag based on the result of
an expression (see Expressions)
Note that the 'value' attribute has a slightly different behavior for
Internal tags than for regular PLC tags:
For PLC tags the result of the expression is first written to the PLC
already converted to the relevant type and appropriately limited and
descaled according to the 'bounds' and 'scale' attributes. On
reading, the tag value is scaled back to the engineering unit. As a
consequence a tag may end having a slightly different value after
that. For example a Tag of type INT having scale={0,10,0,1}; will
become 1.2 when assigning 1.234 to it through a 'value' change. Of
course, the value in the PLC will become 12.due to the scaling and
type conversion.
On PLC writes involving STRINGS implicit conversions will also be
performed if possible. For example, the STRING "2.3" will be
converted to the number 2.3 upon writing a REAL tag. Similarly, the
number 2.3 will result to the sequence of characters "2.3" when
writing to a STRING tag.
For INTERNAL tags no type or scale conversion is performed on the
result of the 'value' expressions. Internal tags are just given the
result of the expression as it evaluates. Thus, the 'scale' and
'bounds' attributes will have no effect. Even the tag type is ignored to
the effects of the assignment and the variable may hold a
completely different type.
The following considerations also apply:
INTERNAL tags containing tag references in its 'value' expression
can not be user writable and will ignore an eventual 'write_access'
attribute (NOTE: this restriction was removed after version
1.5).Despite the preceding consideration, INTERNAL tags will
preserve the meaning of the 'write_access' attribute if their 'value'
expression represents a constant value, in such case the expression
will provide the initial value for the tag.
Writable INTERNAL tags will simulate a write-read round on a virtual
PLC taking into account tag type, 'scale' and 'bounds' attributes with
the same effects as a real write-read round as described above.
hidden expression
(boolean) Numeric expression. Will make the row hidden when the result of
the expression is non zero. Hiding all rows in a Section will remove
the entire section including the section title. Hiding all rows/sections
on a page will remove that page from the interface.
Hiding/showing interface elements is fully animated and dynamic on
evaluation of the 'hidden' expression. Dynamic hiding is useful to
switch among several rows that selectively meet an arbitrary
condition, or to force display parts of the interface depending on
user or PLC triggered conditions.
style special
text Attribute containing one of the texts below determining ways to
represent or display the value of a variable.