Rockwell Automation 1794-OF8IH FLEX Isolated Input/Output HART Analog Modules - Manual (Page 115)

Publication 1794-UM065B-EN-E - September 2010
Additional HART Protocol Information 103
Start Character
The start character of a HART message indicates the frame’s format, the
source of the message, and if it is using burst mode.
HART Address
The Smart Transmitter Interface addresses HART field devices using either a
short or long frame address format, as specified by the HART delimiter byte.
A short frame address is one byte long. A long frame address is five bytes long
and includes a unique 32-bit identifier encoded within each field device by the
manufacturer.
HART field device addressing is device dependent. Some devices do not
support long frame addressing while others only recognize short frame
addressing for HART Command 0. In this situation, use HART Command 0
to determine the long frame address, and then use long frame addressing for al
other HART commands. Refer to the documentation provided with your field
device for details about the addressing formats it supports.
HART Command
This one-byte field specifies the HART command that is to be sent by the
Smart Transmitter Interface to the field device. Many commands are device
dependent. Refer to the documentation provided with your field device for
details about the commands supported. Set this field to a device-recognizable
command before sending the packet to the Smart Transmitter Interface.
Start Character Byte Definitions
Frame Type Short Frame Addressing
(hex) Long Frame Addressing
(hex)
Master To Slave 02 82
Slave To Master 06 86
Burst Mode From Slave 01 81
Representative of HART Universal Commands
Universal Command
(dec) Description Expected Response
0 Read unique indentifier Unique 32-bit device indentifier,
revision levels, number of
preambles required
1 Read primary variable Primary variable in floating point
(IEEE 754 format)
2 Read primary variable
current and percent of range Primary variable in milliamperes
and percents