National Instruments FP-3000 - Manual (Page 72)

Chapter 4 Block Reference
FieldPoint FP-3000 User Manual 4-20 www.ni.com
discussed above). The confirmation message confirms that the message has
made it across the bus to the host. It does not indicate acknowledgment by
the operator. Until the device receives the confirmation message, the alarm
or event is considered to be unreported. In the case where a block has no
alarm linkage, the device waits to report the alarm or event until the linkage
is established. If an alarm is unable to be reported to a host, the Active/Clear
state of the alarm stays constant until the alarm can be reported.
TIME_STAMP
The time the alarm was detected by the FP-3000. In F O U N D A T IO N Fieldbus,
all devices share a common sense of time, as published by the time master
on the bus. This shared sense of time is used to timestamp alarm conditions
as they occur, rather than when they are reported.
SUBCODE
For Block alarm, the subcode of the last error condition detected. The
Block alarm, shared by all F
O U N D A TIO N Fieldbus function blocks in the
FP-3000, is unique in that there are multiple conditions that can cause it to
go active and clear. Any error condition reported in the
BLOCK_ERR
parameter of the block causes the block alarm to go active. The alarm does
not clear until the last error condition in
BLOCK_ERR has been resolved. To
indicate which error condition the BLOCK_ALM is reporting, the SUBCODE
subfield of the parameter is set to indicate the block error condition causing
the fault. If additional error conditions are detected, the
SUBCODE and
TIME_STAMP are updated to reflect the latest condition detected, but the
alarm will not be reported again until every error condition has been
resolved and a new condition triggered.
VALUE
For limit alarms, the value of the parameter causing the alarm condition
(the Process Variable). For update events, the index of the modified static
parameter.
Status and Mode Handling Overview
Status and mode handling are crucial aspects of developing a distributed
control application. Mode refers to the mode of operation of a function
block. Allowable modes depend on the type of block, but generally include
Out of Service mode, Manual mode, and Automatic mode.