National Instruments FOUNDATION NI-FBUS Hardware And Software User Manual page 108

Chapter 6 NI-FBUS Function Reference
Description
nifReadObject
parameters from devices.
• If is the descriptor of a link, then
ud
BLOCKTAG.PARAM_NAME
• If is a session descriptor, then all links are searched for the given
ud
BLOCKTAG.PARAM_NAME
tags are located on the bus. Index access is not allowed for session descriptors.
• If is the descriptor of a general function block application VFD, then name must be
ud
in the format
• If is the descriptor of a function block,
ud
• If is the descriptor of a function block, and the
ud
NIFB_INDEX_SUBINDEX
parameter within the block. Relative indices start at 1 for the first parameter.
• In all descriptor cases, you can expand
to represent a named element of a named structure.
In each case,
determine the size of the object beforehand, possibly with a call to
If the object is larger than the buffer size specified in
Manager returns an error, and none of the data in the buffer is valid.
Refer to Table 6-5 for an explanation of how to use macros to specify the parameter.
The data
nifReadObject
must accomplish conversion of the data to the internal format of your processor and compiler.
Return Values
E_OK
E_INVALID_DESCRIPTOR
E_NOT_FOUND
E_OBJECT_ACCESS_DENIED
E_MULTIPLE
E_BUF_TOO_SMALL
NI-FBUS Hardware and Software User Manual
reads the values of objects such as block parameters or communications
.
. The call fails if multiple identical
BLOCKTAG.PARAM_NAME
macro is used, the index specified is the relative index of the
can represent either a variable or a variable list object. You should
name
returns is in Fieldbus Foundation FMS Application format. You
The call was successful.
The descriptor does not correspond to a VFD or function block.
This descriptor is no longer valid.
The referred object does not exist.
The NI-FBUS Communications Manager interface does not have
the required privileges. The access group you belong to is not
allowed to acknowledge the event, or the password you used is
wrong.
The NI-FBUS Communications Manager found more than
one identical tag. The function failed.
The object is larger than your buffer.
must be in the format
name
.
must be in the format
name
NIFB_INDEX
itself to
PARAM_NAME
, the NI-FBUS Communications
length
6-46
BLOCKTAG.PARAM_NAME
PARAM_NAME
or
format
STRUCT.ELEMENT
nifGetObjectSize
.
.
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