Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 117)

Rockwell Automation Publication 1756-UM533C-EN-P - February 2011 117
Configure the Modules with RSLogix 5000 Software Chapter 7
How the Module Automatically Collects Data
The ControlLogix HART analog module automatically sends HART messages
to characterize the HART field device and collect the dynamic variables. It also
collects additional status information when the device indicates it is available.
When the device indicates its configuration has changed, HART messages are
sent to reread the configuration information so that a current copy is cached in
the modules.
The diagram on page 118 shows the general flow of the start-up characterization,
response to a new configuration, and cyclic scanning of dynamic variables. Not
shown are periodic checks of the current and reading the additional status
information.
In addition to the HART activities outlined in the diagram, if there are HART
pass-through messages to send, they are interleaved in the auto scanning. Logix
controllers can send pass-through messages using CIP MSG instructions, and
Asset Management systems can send them. See
Chapter 8 for more information.
HART messages are only sent on one channel at a time when you are using the
1756-IF8H or the 1756-OF8H modules. When you are using the 1756-IF16H
module, messages are sent on all channels simultaneously.
If the HART field device configuration is changed—from a handheld, asset
management, or device faceplate—cyclic reading of the Dynamic Variables pauses
briefly while the configuration changes are assimilated. The
HART.ChxDeviceStatus.ConfigurationChanged status is set when the updated
configuration is retrieved from the HART field device and stored in the module
to indicate that new data is available for GetDeviceInfo CIP MSG.
See Getting HART Data By Using CIP MSG on page 121 for more information,
and specifically page 133 for HART pass-through schedule choices.