Echelon i.LON 1000, Руководство пользователя, Страница: 86 / 126

10-14 Advanced Usage of the
<iLonWeb>
HTML Tag
displays the data as hexadecimal byte values, with each byte separated by a space. The
“
RAW_HEX_PACKED
” format displays each byte as a two-digit hex value, with no spaces in
between the byte values.
The “
RAW_HEX_PACKED
” format is the default format for non-SNVT network variables that
do not specify a format.
PROPAGATE:
The PROPAGATE: attribute allows you to specify whether a value should be transmitted
across the network immediately, or buffered. For example:
<iLonWeb FUNC=TextField
SYMBOL=NVL_DigitalOut!FIELD:value!PROPAGATE:TRUE></iLonWeb>
The PROPAGATE: attribute defaults to
TRUE
when a tag references a complete network
variable, and
FALSE
when a tag references a network variable field. Network variable fields
may not be manipulated individually over the L
ON
W
ORKS
network—the entire network
variable value can be changed, but not one field at a time. These default settings are
designed to assure that updates are consistently delivered for the specified network variable.
In addition, it is typically more efficient to update several fields and propagate the network
variable once, instead of causing propagation for each field update.
If your HTML form sets a network variable value field-by-field, the propagate attribute
should be set to
FALSE
for all of the network variable field tags in the form except the last
one. The last propagate attribute of
TRUE
will cause the network variable value to be
propagated over the network. Note that if you set propagate to
TRUE
for each field, some
fields may contain indeterminate values in the network variable update, which should not be
propagated.
WAIT:
The WAIT: attribute allows you to specify whether to wait for the acknowledgement of a
write command. Using the wait feature, you may test whether a local output network
variable’s update is acknowledged by the remote inputs. The test will only be valid if the
local output network variable is connected to one or more remote network variables by the
acknowledged address services. If the connection is made by an unacknowledged message
service, the test will always return a positive response, even if the network variable update
did not reach its target.
To perform the test:
1.
Set the WAIT: attribute to TRUE by adding
!WAIT=TRUE
to the web tag responsible for
writing the network variable. This causes the data server to wait for an
acknowledgement (ACK) or failure from the network variable before returning from
processing that field.
2.
Modify the web page so it reads back the results of the acknowledgement. Following the
update tag, place a
ShowValue
tag for the same network variable and specify a field
name of “$ErrStatus” (!
FIELD:$ErrStatus
). This field returns the value of the network
variable’s error status.
If all of the expected acknowledgments were received, the returned error string will be
empty. If any acknowledgements failed, the string “No acknowledgement from remote
network variable” will be returned. Since an empty error string will be returned on success,