Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 123)

Rockwell Automation Publication 1756-UM533C-EN-P - February 2011 123
Getting HART Data By Using CIP MSG Chapter 8
CIP Services to Access
Common HART Data You can get the following kinds of HART data easily from the HART object:
• HART field device information - Similar to that displayed on the
Module Properties HART Device Info tab of RSLogix 5000 software.
• Additional status - HART devices that support extended diagnostics can
indicate in their Field Device Status that some additional diagnostic
information is available.
• Dynamic variables - The same PV, SV, TV, FV that are in the input tag.
The mapped Device Variable Code and the engineering units are included.
The data in these commands is returned in the format used by Logix controllers,
so it is very easy to use in your control program. HART data is natively in a
different format, called big-endian, but the module converts the values in these
messages for you.
See the tables that list the data in the CIP messages and the example of getting the
Device Info.
In the following sections the definition CMD#0 byte 3, for example, means
HART command 0, byte 3. If your field device user manual includes information
about HART command responses, this information will be helpful to you.
Consult the HART protocol specification for further information on HART
commands. See
Appendix C on page 193 for more information.
Read Dynamic Variables (Service Code = 16#4B)
These tables show the request and reply packet structures for the Read Dynamic
Variables service.
Table 31 - Request Packet
Offset Field Data Type Definition
No request data
Request size = 0 bytes
Table 32 - Reply Packet - Request Failed
Offset Field Data Type Definition
0 Status USINT Command status
1 Pad Pad byte
Reply size = 2 bytes
Request Failed