Chapter 6
NI-FBUS Function Reference
©
National Instruments Corporation
6-21
NI-FBUS Hardware and Software User Manual
nifOpenVfd
Purpose
Returns a descriptor representing a Virtual Field Device (VFD).
Format
nifError_t
nifOpenVfd (
nifDesc_t ud,
char *vfdTag,
nifDesc_t *out_ud)
nifError_t
nifOpenVfd (
nifDesc_t ud,
NIFB_ORDINAL(n),
nifDesc_t *out_ud)
Input
ud
A valid physical device descriptor.
vfdTag
The tag of the VFD. To access by ordinal number within a
physical device, use the
ORDINAL
macro in the
nifbus.h
header file.
Output
out_ud
A descriptor for the VFD you request.
Context
Physical device.
Description
nifOpenVfd
returns a descriptor for the VFD you specify. More than one VFD can reside
within a physical device. You must pass a valid physical device descriptor to this function.
There are two ways to specify the VFD: by tag and by ordinal number. To open the VFD by
its tag, you must set the
vfdTag
parameter to the current tag of the VFD. The NI-FBUS
Communications Manager returns an error if it finds more than one VFD with the same tag.
You can obtain the list of VFD tags within a specified physical device with a call to
nifGetVFDList
.
To open the VFD by its ordinal number, use the
NIFB_ORDINAL
macro. The first VFD of your
application in a physical device has the ordinal number zero. Notice that the Management
VFDs are not included in the ordinal numbering scheme.
