Chapter 4
NI-FBUS CM Software
©
National Instruments Corporation
4-5
NI-FBUS Hardware and Software User Manual
The NI-FBUS Communications Manager sends the communication
acknowledgment to the device automatically. The NI-FBUS
Communications Manager provides a separate function,
nifAcknowledgeAlarm
, to send the operator acknowledgment.
Similarly,
nifWaitTrend
lets you wait for a trend from any device in
a link, any function block in a physical device, or a specific function
block, depending on the type of descriptor you pass to it. When the
NI-FBUS Communications Manager receives a trend, it returns a structure
containing information about the trend along with the trend data itself.
nifWaitAlert
,
nifWaitAlert2
, and
nifWaitTrend
wait until an alert
or trend is received before returning, so it might be preferable to have
separate threads invoke these functions.
Device Description Functions
The NI-FBUS Communications Manager gives your applications access to
device descriptions, which are binary files that describe the characteristics
of blocks and parameters. Your application can use the NI-FBUS function
nifGetObjectAttributes
to decode attributes of parameters including
data type, data size, help strings, and other attributes defined in the
Device
Description Language Specification
document. In addition, device
description symbol files are used automatically to assist in allowing your
applications to access parameters by name.
The NI-FBUS Communications Manager ships with device descriptions
for all standard F
OUNDATION
™
Fieldbus function blocks. The NI-FBUS
Communications Manager provides attributes for the parameters of all
standard
function blocks, even if the device manufacturers for your devices
did not provide device descriptions. However, to get the attributes of
parameters of nonstandard (not F
OUNDATION
™
Fieldbus-defined) blocks, the
NI-FBUS Communications Manager requires that the device manufacturer
provide the device description.
NI-FBUS supports device description menus and methods. When
NI-FBUS attempts to locate a device description file (
.ffo
and
.sym
) for
a device, it uses the file with the latest device description revision for a
given
MANUFAC_ID
,
DEV_TYPE
, and
DEV_REV
. For more information about
device descriptions, refer to the
F
OUNDATION
TM
Fieldbus Overview
document
or your Getting Started manual.
