Comparison Between NI-VISA and NI-488.2 APIs

NI-VISA 15.0 Help

Edition Date: June 2015

Part Number: 370131S-01

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For GPIB users who are familiar with NI-488.2, the following table shows several common, but not all, NI-488.2 device-level function calls and the corresponding VISA operations. As you can see, the APIs are almost identical. The difference is that VISA is extensible to additional hardware interfaces. Therefore, if you are programming multiple devices that communicate over more than one bus type, it might be easier to use VISA for your entire system.

NI-VISA and NI-488.2 Functions and Operations

C NI-488.2 Device Function C VISA INSTR Operation LabVIEW NI-488.2 Device Function LabVIEW VISA INSTR Operation
ibdev viOpen <no equivalent>
VISA Open
ibonl viClose <no equivalent>
VISA Close
ibwrt viWrite
GPIB Write

VISA Write
ibrd viRead
GPIB Read

VISA Read
ibclr viClear
GPIB Clear

VISA Clear
ibtrg viAssertTrigger
GPIB Trigger

VISA Assert Trigger
ibrsp viReadSTB
GPIB Serial Poll

VISA Read STB
ibwait viWaitOnEvent
Wait for GPIB RQS
Wait for RQS
ibconfig viSetAttribute
GPIB Initialization

VISA Property Node

One difference in the event mechanism between NI-488.2 and VISA is worth noting. In VISA, you must always call viEnableEvent() prior to being allowed to receive events. While this was not the case with NI-488.2, this is required in VISA to avoid the race condition of trying to wait on events for which the hardware may not be enabled. Thus, you should enable the session for events not just immediately before calling viWaitOnEvent(), but before the device has even been triggered or configured to generate a service request event.

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