Filter
Top Products
Chapter 3 Developing Your NI-488.2 Application
© National Instruments Corporation 3-5 NI-488.2 User Manual for Windows
Board-level functions that an NI-488.2 application might use include the
following—
ibcmd
,
ibrd
,
ibwrt
, and
ibconfig
. For a detailed list, refer
to the NI-488.2 online help. For instructions on accessing the online help,
refer to the Using the NI-488.2 Documentation section in About This
Manual.
Using Multiple Interfaces and/or Multiple Devices
When your system includes an interface that must access multiple devices,
use the multi-device NI-488.2 calls, which can perform the following tasks
with a single call:
• Find the Listeners on the bus using
FindLstn
.
• Find a device requesting service using
FindRQS
.
• Determine the state of the SRQ line, or wait for SRQ to be asserted
using
TestSRQ
or
WaitSRQ
.
• Address multiple devices to receive a command using
SendList
.
You can mix board-level traditional NI-488.2 calls with the multi-device
NI-488.2 calls to have access to all the NI-488.2 functionality.
Checking Status with Global Variables
Each NI-488.2 API call updates four global variables to reflect the status of
the device or interface that you are using. These global status variables are
the status word (
ibsta
), the error variable (
iberr
), and the count
variables (
ibcnt
and
ibcntl
). They contain useful information about the
performance of your application. Your application should check these
variables after each NI-488.2 call. The following sections describe each of
these global variables and how you can use them in your application.
Note
If your application is a multithreaded application, refer to the section Writing
Multithreaded Win32 NI-488.2 Applications in Chapter 7, NI-488.2 Programming
Techniques.
Status Word (ibsta)
All NI-488.2 calls update a global status word,
ibsta
, which contains
information about the state of the GPIB and the GPIB hardware. The value
stored in
ibsta
is the return value of all the traditional NI-488.2 calls,
except
ibfind
and
ibdev
. You can examine various status bits in
ibsta
and use that information to make decisions about continued processing. If