Spectrum Controls 1756sc-OF8H Series A - Manual (Page 98)

84 ControlLogix ™ Analog HART Modules
ignore the command and continue operation. This state of operation
will not be maintained after power-up or when configuration changes.
DEAD will be sent back if any of the following conditions is true:
• Command and HART Channel number are both valid.
• HART channel is not enabled
• HART communication has not been established, meaning that the 5-
byte unique address has not been determined yet, or the module is still
obtaining device information.
• All other conditioned not generating SUCCESS.
HART Pass-Through Command
The HART Pass-Through Command can be used to send any HART
command including, universal, common practice or device specific, directly
to a field device. The module in this case could be considered a HART
bridge. There can be two (2) instances of a HART pass-through message
being serviced, meaning the pass-through message queue is 2 deep. The
HART pass-through response will be queued the moment the command is
received, if the queue spaces are not already in use, and be dispatched
after at least a full scan is done. In another word, after servicing a pass-
through, the HART module will make sure all enabled HART channels
have updated variable values before another pass-through is placed into
service.
All HART pass-through commands require a series of messages to be
exchanged. First, a pass-through command request must be sent to the
HART module to initiate the pass-through command. The HART module
will respond to the command request with a command request reply that
includes a handle that can be used to obtain the pass-through message
response. Once the handle is received, the user may issue a Get
Command Query to obtain the status of the pass-through command and
the pass-through command response data, if it is available.
There is a handle timeout associated with the final reply message. After
the HART module obtains the requested information from the HART
device, it will start the HandleTimeout (as defined in the Configuration
Tag) timer. The reply message will be kept persistent during the
HandleTimeout period. When the timeout occurs the reply message will
be discarded, and another pass through message will be serviced without
being rejected. The user defined Handle-Timeout is in the range of 1 to
255 seconds.