Discover HART Commands Now!

HartCommands

Data Link Layer Commands

These commands support the establishment of a communication connection between the Master and the Field Device, and modifying the FSK preamble length.

  • Command 59 Write Number of Response Preambles
  • Command 72 Squawk
  • Command 73 Find Device
  • Command 74 Read I/O System Capabilities
  • Command 75 Poll Sub-Device

Primary Variable Range Commands

The Primary Variable is always associated with the first Analog Channel of a device. Since the 4-20mA signal conveys a single dynamic value using the analog signal, these Common Practice Commands allow the relationship between the analog signal and the Primary Variable digital value to be defined.

  • Command 35 Write Primary Variable Range Values
  • Command 36 Set Primary Variable Upper Range Value
  • Command 37 Set Primary Variable Lower Range Value

Loop Current Commands

Supporting the analog 4-20mA Loop Current is a fundamental requirement for HART compatible Field Devices. The commands in this section allow loop current values to be simulated and allows the Field Device’s perceived loop current value to be calibrated. With respect to the Loop Current, the only difference between a transmitter and an actuator is that the Loop Current value is what a transmitter thinks it is outputting and what an actuator believes it is measuring.

  • Command 40 Enter/Exit Fixed Current Mode 
  • Command 45 Trim Loop Current Zero 
  • Command 46 Trim Loop Current Gain

Device Management Commands

The Common Practice Commands support routine device management functions, like forcing a self test or performing a device reset.

  • Command 38 Reset Configuration Changed Flag 
  • Command 41 Perform Self Test 
  • Command 42 Perform Device Reset 
  • Command 48 Read Additional Device Status 
  • Command 71 Lock Device • Command 76 Read Lock Device State

Transducer Trim Commands

This section includes four commands to allow the adjustment or “trim” of a Device Variable. This allows a measurement to be trimmed linearly, assuming the measurement has already been corrected for the transducer characteristics. Transducer characterization is considered a device-specific operation and is beyond the scope of this Specification. Furthermore, transducer and device characterization is not generally possible in a field environment.

  • Command 80 Read Device Variable Trim Points 
  • Command 81 Read Device Variable Trim Guidelines 
  • Command 82 Write Device Variable Trim Point • Command 83 Reset Device Variable Trim

Mapping Process Variables Commands

All HART compatible Field Devices are required to return the Primary, Secondary, Tertiary, and Quaternary Variables. These are collectively called the Dynamic Variables. In addition, all HART compatible Field Devices contain Device Variables. Simple Field Devices may use only Dynamic Variables and not expose the underlying Device Variables at the Protocol Application Layer interface. In simple devices the mapping of Device Variables to Dynamic Variables is fixed. More sophisticated devices allow this mapping to be configured

  • Command 50 Read Dynamic Variable Assignments 
  • Command 51 Write Dynamic Variable Assignments 

Primary Variable Commands

Due to its connection to Loop Current, the Primary Variable is an essential Application Layer data item. Consequently, there are Common Practice Commands supporting the configuration of the Primary Variable.

  • Command 34 Write Primary Variable Damping Value 
  • Command 43 Set Primary Variable Zero
  • Command 44 Write Primary Variable Units 
  • Command 47 Write Primary Variable Transfer Function • Command 49 Write Primary Variable Transducer Serial Number

Device Variable Commands

Device Variables represent the device’s connection to the process. While simple devices may not expose their Device Variables, all HART compatible Field Devices contain them. Several important features of the HART Protocol rely on Device Variables

  • Command 33 Read Device Variables 
  • Command 52 Set Device Variable Zero 
  • Command 53 Write Device Variable Units 
  • Command 54 Read Device Variable Information 
  • Command 55 Write Device Variable Damping Value 
  • Command 56 Write Device Variable Transducer Serial No. 
  • Command 79 Write Device Variable 
  • Command 113 Catch Device Variable • Command 114 Read Caught Device Variable

Burst Mode Commands

The protocol supports the publishing of cyclical process data via burst mode operation. In this mode, a Field Device is instructed to publish the response to a command continuously without any further Master action. If a Field Device supports Burst Mode, then all commands in this section must be implemented.

  • Command 105 Read Burst Mode Configuration 
  • Command 107 Write Burst Device Variables 
  • Command 108 Write Burst Mode Command Number • Command 109 Burst Mode Control

Analog Channel Support Commands

All HART devices support Analog Channel 0 corresponding to the Loop Current. However, some devices support several Analog Channels (inputs to or outputs from the Field Device).

  • Command 60 Read Analog Channel And Percent Of Range 
  • Command 62 Read Analog Channels 
  • Command 63 Read Analog Channel Information 
  • Command 64 Write Analog Channel Additional Damping Value 
  • Command 65 Write Analog Channel Range Values 
  • Command 66 Enter/Exit Fixed Analog Channel Mode 
  • Command 67 Trim Analog Channel Zero 
  • Command 68 Trim Analog Channel Gain 
  • Command 69 Write Analog Channel Transfer Function • Command 70 Read Analog Channel Endpoint Values