Rockwell Automation 1794-APBDPV1 FLEX I/O PROFIBUS Adapter User Manual - Manual (Page 137)

Publication 1794-UM064B-EN-P - May 2014
124 Additional HART Protocol Information
Byte Count
This one-byte field indicates the number of bytes to follow this field excluding
the check byte. Valid values are 0 to 113. Insert the number of bytes required for
this packet before transmitting it.
Data
This field specifies a number of data bytes associated with the command number
given in the command field. Set the number of data bytes to the appropriate value
for the command in question. The valid range is from
0 to 113. Only use this field when writing data to the HART device.
Check Byte
The Smart Transmitter Interface calculates the value of this field and transmits it
to the field device as the last byte of a packet. The field device verifies the integrity
of the received data packet by checking this byte. Since the Smart Transmitter
Interface calculates this byte, you can set this field to a null (00).
Response Code
This two-byte code contains the HART field device status as sent by that device.
Field devices detecting a communications error set the most significant bit, bit 7,
of the first byte and identify the error in the other seven bits. If the last message
was received without error, the field device will clear bit 7 and return a
device-dependent response in the other seven bits.
The second byte of this response code returns the operating status of HART field
devices. This byte may default to 0 when a communications error occurs as
indicated by bit 7 of the first byte being set.
3 Read dynamic variables and
primary variable current Primary variable and up to 4
predefined dynamic variables
6 Write polling address Assigned polling address - short form
11 Read unique identifier
associated with tag Unique 32-bit device identifier,
revision levels, number of preambles
required
IMPORTANT The host processor ignores any values in the data field when a
communications error is detected.
Representative of HART Universal Commands
Universal Command
(dec) Description Expected Response