User guide

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This chapter discussed the HART protocol and provides references for

additional information about the protocol. This chapter provides:

• HART Protocol background information.

• Common Practice command sets.

• Extended command sets.

• References to additional information.

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HART Field Communications Protocol is widely accepted in the industry

as the standard for digitally enhanced 4-20mA communication with smart

field instruments. The HART Protocol message structure, command set

and status are discussed in this chapter.

The HART Command Set is organized into three groups and provides

read/write access to a wide array of information available in smart field

instruments.

Universal Commands provide access to information that is useful in

normal plant operation such as the instrument manufacturer, model, tag,

serial number, descriptor, range limits, and process variables. All HART

devices must implement Universal Commands.

Common Practice Commands provide access to functions, which can

be carried out by many devices though, not all.

Device Specific Commands provide access to functions that may be

unique to a particular device.

Appendix D