SLAAEH0 November   2023 AFE781H1 , AFE782H1 , AFE881H1 , AFE882H1 , DAC161P997 , DAC161S997 , DAC7750 , DAC7760 , DAC8740H , DAC8741H , DAC8742H , DAC8750 , DAC8760 , DAC8771 , DAC8775

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction to the HART Protocol
    1. 1.1 Different Forms of the HART Protocol
    2. 1.2 HART as an Enhancement to the 4-20 mA Loop
    3. 1.3 The HART FSK Signal
    4. 1.4 HART Configurations
    5. 1.5 HART Protocol Structure
      1. 1.5.1 HART Communication
      2. 1.5.2 HART Bytes
      3. 1.5.3 HART Data Frame Structure
        1. 1.5.3.1 HART Start Byte
        2. 1.5.3.2 HART Device Addressing
        3. 1.5.3.3 HART Commands
  5. 2HART Protocol and Test Specifications
    1. 2.1 The OSI Protocol Model
    2. 2.2 HART Protocol Specifications
    3. 2.3 HART Test Specifications
  6. 3TI HART Enabled Devices
    1. 3.1 TI DACs with HART Connections
    2. 3.2 TI HART Modems
  7. 4Conclusion
  8. 5References

1.4 HART Configurations

There are two basic methods of connecting to a HART device to the control system. Figure 1-5 shows a point-to-point connection of a control to HART enabled field transmitter device

GUID-20231026-SS0I-X13L-K5HS-43TC5KMDKVCR-low.svg Figure 1-5 Point-to-Point Connection for a HART Host and a HART-Enabled Field Transmitter

A host can have multiple inputs through a switch. When there is communication, each input has a power supply and receiver. The host sends commands and receives data from a single field device. A secondary host can be used to send commands and receive data, but there is a single field device on the loop.

The second basic method of connecting a HART device to the control system is multi-drop mode. In multi-drop mode, multiple field devices are connected in parallel. Using this mode, there is no primary variable and the current is fixed at 4 mA for each field device. Figure 1-6 shows multiple field transmitters set up in multi-drop mode.

GUID-20231026-SS0I-LLDG-5VKN-B2T6WSBTCNR9-low.svg Figure 1-6 Field Transmitters Set Up in HART Multi-Drop Mode

Each of the devices are identified through a unique address. In this way, the host can communicate with an individual device on the loop. Different revisions of HART allow for different numbers of addresses:

  • Address 0: Default address for point-to-point devices
  • Addresses 0 to 15: Address range for HART revision 5 or earlier for multi-drop loop devices
  • Addresses 0 to 63: Address range for HART revision 6 or newer for multi-drop loop devices