Spectrum Controls 1734sc-IE2CH - Manual (Page 43)

Chapter 4: IExCH and HART 4-3
User’s Manual Pub. 0300257-01 Rev. A
4.2.1 Auto-Scanning of Dynamic HART Variables (PV, SV, TV, FV)
The module will continuously send Cmd 3 or Cmd 9 to the HART device connected on a
channel. Which command is sent is determined by the HART Universal revision number
of the HART device. If the device has a revision of 6 or greater then Cmd 9 is used,
otherwise for HART revision 5 devices Cmd 3 is used. The advantage of Cmd 9 is that it
contains a “Health Status” byte for each of the 4 dynamic variables that it returns. The
Dynamic variables and the status bytes are published in the module input tags. See
Section 3.6 for more information.
Device
in scan
list?
Send Command 0
Read Unique Identifier
Send Command 3 or 9
to read Dynamic
process variable
Reply?
Update Input Tag
New
Config.
Indicated
Remove device from
scan list
Reply?
Read configuration
information, such as
tag, units, range, etc.
Signal configuration
changed in input tag
Put device in scan list
Read configuration
information, such as
tag, units, range, etc.
Signal configuration
changed in input tag
Process 1
pass-through message
Yes
No
Yes
Yes
Yes
No
No
No
Figure 4-2 (Connect Cycle)