Spectrum Controls 1769sc-HART Modules - Manual (Page 104)

Compact IO™ Isolated HART Analog Input Module
User's Manual 0300215-03 Rev. A
7-36
Table 7-15 (HART Pass-Through Request Reply)
HART pass through command request – reply packet structure
Field Value Definition
HART Channel Number 0x00 – 0x03 (1 byte) Module input
channel number for
HART command
Status (1 byte)
32 = Busy (Queue is already full).
33 = DR_INITIATE
35 = DR_DEAD (bad request)
Command status
Count (1 byte) Set to 1
Handle (1 byte)
0 (bad when status is DR_DEAD)
1-255 (good)
The handle for
command complete
query
The command status, the second byte in the reply packet for this module specific
command, can return two different responses, INITIATE, and DEAD. These responses
echo the state of the module at the time the command is sent. The conditions for each
response are as follows:
INITIATE will be sent back under the following conditions:
•
Command and HART Channel number are both valid.
•
HART channel is enabled and communication has been established, meaning at
least the device addressing information is available.
•
Handle is available, meaning no pending handle is still active.
•
HART channel is doing regular data sampling only. No pending device
information gathering is active.
•
No pending pass-through handle is active, meaning handle timeout has not
occurred yet.
•
Device address and delimiter are valid.
•
Received CIP word count is large enough for the entire command packet.
DEAD will be sent back if any of the following conditions are true:
•
Command or HART Channel number is invalid.
•
HART channel is not enabled.
•
HART communication has not been established, meaning that the 5-byte unique
address has not been determined yet.
•
The channel is currently updating device information. Theoretically, pass-
through command can be safely accepted after successfully receiving Command
0, but for simplicity, we'll track update of the device information as a whole.
•
All other conditioned not generating INITIATE.
After the pass-through response is sent with a valid handle and a response value
indicating (33) INITIATE, the user can retrieve the data associated with the handle using
the following command message.