Flowserve MX HART Field Unit - Manual (Page 34)

MX/QX HART Field Unit FCD LMENIM2340-00 – 1/14
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There must be only one burst mode device active on the communication link at any given time. This is because the
Master must adapt its operation to ensure correct bus arbitration, because the token passing sequence is fundamentally
changed.
3.5.3.1 Update Periods
The host application or control system may set the update periods for the Limitorque MX/QX field device to the
following allowed values: 0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0, and 60-3600 seconds.
If a setting is requested that is different from those indicated above, the HART device must correct the setting and send
response code 8 “Update Times Adjusted” in its response message. The update time returned in the response message
will reflect the adjusted update time the device is using.
When enabling burst messaging, the device takes control of the Token Passing Layer bursting out the default burst
message with no less than “Link Grant Time” (approximately 75 ms) between bursts. This Link Grant Time allows
another master to take over the bus and transmit a message. If only one burst message is enabled, it is the default
burst message. If more than one burst message is enabled, the burst message with the shortest update period is the
default burst message.
On a Token Passing Data-Link burst, messages are used both to publish data and to pass the token. Therefore, the
default burst message will always burst with approximately 75 ms between bursts, regardless of what value is set for
the “Update Period” of the default burst message. If more than one burst message is enabled, the other (not default)
burst messages will be burst based on their Update and Max Update Periods.
3.5.3.2 Commands Supported for Burst Message
• Command 1 Read Primary Variable
• Command 2 Read Loop Current and Percent of Range
• Command 3 Read Dynamic Variables and Loop Current
• Command 9 Read Device Variables With Status
• Command 33 Read Device Variables
• Command 48 Read Additional Device Status
• Command 93 Read Trend
3.5.3.3 Configuring a Device for Burst Mode Operation
Burst messages can be configured from the DD menu Device Setup->Wired Hart Board->Configuration->Burst
Messages as follows: