Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules User Manual
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Rockwell Automation Publication 1756-UM533C-EN-P - February 2011
Chapter 8
Getting HART Data By Using CIP MSG
If your input tag includes the HART PV data, a status indicator
HART.ChxDeviceStatus.MsgReady tells your program a HART reply is ready to
retrieve with the Pass-through Query command.
The CIP reply from the Init service includes a number called the handle. This
handle identifies the HART message that was placed in a queue for transmission
to the field device. When the reply is received and MsgReady is set to 1, your
Logix controller should send a Query containing that same handle to retrieve the
HART reply. The reason these steps are necessary is that it can take a long time
for the HART command to be transmitted and a reply received. If all eight
channels are in use, the time for a reply would be about 10 seconds if there was no
other pass-through traffic.