FIELD
IN_SUMMARY "summary_tag" Column Width
HOST_DATA_ORDER | NETWORK_DATA_ORDER
A FIELD statement always does the following:
Names a field
Defines the size of that field
Generates material to display the content of the field in the Decode Pane
Normally it also:
Moves the pointer forward to the next field
Optionally it may:
Reposition the pointer prior to decoding
Inhibit updating of the pointer (leaving it pointing to the same field)
Make decoding of the field conditional
Massage the field value before storing it
Display something in the Summary Pane
Check the content of the field
Tag the field for use in filtering and other operations
Invoke a method that verifies a frame check sequence (CRC or checksum)
Store a value in a variable
Formally, the composition of a FIELD statement is as follows:
FIELD field_name
[START_BIT StartBitMethod]
SizeMethod
[<Conditional-Clause>: IF [NOT] BooleanMethod [ELSE_SKIP
SizeMethod] | PRINT_IF [NOT] VerifyMethod]
[<Retrieve-Clause>: RETRIEVE RetrievalMethod [ALSO
RetrievalMethod]*]
[<Processing-Clause>: PROCESSING RetrievalMethod [ALSO
RetrievalMethod]*]
FormatMethod [ALSO FormatMethod]
[IN_SUMMARY|IN_SUMMARY_ONLY|IN_COLLAPSED "summary_tag"
column_width]
"detail_tag" | SUPPRESS_DETAIL
[<Tag-Clause>: TAG "tag"]
[MARGIN_TEXT FormatMethod]
[INFO]
[NO_MOVE]
[HOST_DATA_ORDER | NETWORK_DATA_ORDER]
[<Verify-Clause>: VERIFY|SUPPRESS_IF_VERIFIED [NOT]
VerifyMethod [ALSO [NOT] VerifyMethod]]
[<Store-Clause>: STORE variable_name [<Retrieve-Clause>]]
Keywords are shown in all capitals. Optional components are shown in square brackets. Elements in angle brackets are compound components that are described below.
The FIELD statement, as defined here, may seem terribly complicated but, as we have seen in the tutorial, most FIELD statements are really rather simple and straightforward because most or all optional components are unneeded.
Here is the composition of a FIELD with all optional parts omitted:
We will now examine each element in turn. We will start with the required components and then list the optional ones in the order in which they appear.