In HART 7, time value was introduced.
The version 5 and 6 ( *.fms, *.fm6 ) tokenizers do not support TYPE TIME_VALUE so the DD may use TYPE UNSIGNED_INTEGER. For a DD to build all Encoded Formats (*.fms, *.fm6, *.fm8), the variables used for time must be conditionally defined based upon the tokenizer version.
Older HART EDD Host applications which support only Encoded Formats *.fms, *.fm6 can only read a 4 byte unsigned integer in lieu of a time value (which is a 4 byte representation of time).
--------------------------------------------------------------------------------------------------------
For example,
In order to read the “Time Value” for UPDATE_TIME_PERIOD in Command 54 using HART EDD Host applications that only support Tokenizer formats FMS or FM6 (i.e. Version 5 and 6), we will need to create an Unsigned Variable of 4 Bytes
1. Create Two VARIABLEs: TIME_VALUE and UNSIGNED_INTEGER (4)
Create a VARIABLE of type TIME_VALUE and another VARIABLE of type UNSIGNED_INTEGER, 4 bytes and specify each VARIABLE a unique “name” (see below).
Correct
Incorrect
NOTE: All VARIABLE names registered in a HART EDD must only have TYPE defined
2. Create a conditional in each Device Variable collection
Reference the two VARIABLEs created in step 1 (above) in each support Device Variable collection
NOTE: DO NOT create the conditional in the COMMAND
