HART Device Description Language: an example

What does a Device Description look like?

Here is a small sample of DDL, including the description of a Variable, a Menu to get to that Variable, and a Command to write a new value to it.

The phrases in square brackets [xxx] are references to a Standard Dictionary of common phrases, provided as part of the DD scheme, with ready-made translations into several languages.

The punctuation (curly brackets and semicolons) is taken from the "C" programming language. It's quite easy once you've learned it!

Anything between /* and */ is a comment.

VARIABLE low_flow_cutoff
   {
   LABEL "Low flow cutoff";
   HELP "Low Flow Cutoff: the value below which the process variable
     will indicate zero, to prevent noise or a small zero error
     being interpreted as a real flow rate.";
   TYPE FLOAT
      {
      DISPLAY_FORMAT "6.4f";   /* ##.#### */
      }
   CONSTANT_UNIT "%";
   HANDLING READ & WRITE;
   }

MENU configure_input
   {
   LABEL "Configure input";
   ITEMS
      {
      flow_units,          /* variable */
      rerange,             /* edit-display */
      low_flow_cutoff,     /* variable */
      flow_tube_config,    /* menu */
      }
   }

COMMAND write_low_flow_cutoff
   {
   NUMBER 133;
   OPERATION WRITE;
   TRANSACTION
      {
      REQUEST
         {
         low_flow_cutoff
         }
      REPLY
         {
         response_code,
         device_status,
         low_flow_cutoff
         }
      }
   RESPONSE_CODES
      {
      0, SUCCESS,           [no_command_specific_errors];
      3, DATA_ENTRY_ERROR,  [passed_parameter_too_large];
      4, DATA_ENTRY_ERROR,  [passed_parameter_too_small];
      5, MISC_ERROR,        [too_few_data_bytes_received];
      7, MODE_ERROR         [in_write_protect_mode];
      }
   }

Back Top of page