VISA resource names

If you use the method open_resource(), you must tell this function the VISA resource name of the instrument you want to connect to. Generally, it starts with the bus type, followed by a double colon "::", followed by the number within the bus. For example,


denotes the GPIB instrument with the number 10. If you have two GPIB boards and the instrument is connected to board number 1, you must write


As for the bus, things like "GPIB", "USB", "ASRL" (for serial/parallel interface) are possible. So for connecting to an instrument at COM2, the resource name is


(Since only one instrument can be connected with one serial interface, there is no double colon parameter.) However, most VISA systems allow aliases such as "COM2" or "LPT1". You may also add your own aliases.

The resource name is case-insensitive. It doesn’t matter whether you say "ASRL2" or "asrl2". For further information, I have to refer you to a comprehensive VISA description like

VISA Resource Syntax and Examples

(This is adapted from the VISA manual)

The following table shows the grammar for the address string. Optional string segments are shown in square brackets ([ ]).

Interface Syntax
ENET-Serial INSTR ASRL[0]::host address::serial port::INSTR
GPIB INSTR GPIB[board]::primary address[::secondary address][::INSTR]
PXI BACKPLANE PXI[interface]::chassis number::BACKPLANE
PXI INSTR PXI[bus]::device[::function][::INSTR]
PXI INSTR PXI[interface]::bus-device[.function][::INSTR]
PXI INSTR PXI[interface]::CHASSISchassis number::SLOTslot number[::FUNCfunction][::INSTR]
Remote NI-VISA visa://host address[:server port]/remote resource
Serial INSTR ASRLboard[::INSTR]
TCPIP INSTR TCPIP[board]::host address[::LAN device name][::INSTR]
TCPIP SOCKET TCPIP[board]::host address::port::SOCKET
USB INSTR USB[board]::manufacturer ID::model code::serial number[::USB interface number][::INSTR]
USB RAW USB[board]::manufacturer ID::model code::serial number[::USB interface number]::RAW
VXI BACKPLANE VXI[board][::VXI logical address]::BACKPLANE
VXI INSTR VXI[board]::VXI logical address[::INSTR]

Use the GPIB keyword to establish communication with GPIB resources. Use the VXI keyword for VXI resources via embedded, MXIbus, or 1394 controllers. Use the ASRL keyword to establish communication with an asynchronous serial (such as RS-232 or RS-485) device. Use the PXI keyword for PXI and PCI resources. Use the TCPIP keyword for Ethernet communication.

The following table shows the default value for optional string segments.

Optional String Segments Default Value
board 0
GPIB secondary address none
LAN device name inst0
PXI bus 0
PXI function 0
USB interface number lowest numbered relevant interface

The following table shows examples of address strings:

Address String Description
ASRL:: A serial device attached to port 2 of the ENET Serial controller at address
ASRL1::INSTR A serial device attached to interface ASRL1.
GPIB::1::0::INSTR A GPIB device at primary address 1 and secondary address 0 in GPIB interface 0.
GPIB2::INTFC Interface or raw board resource for GPIB interface 2.
PXI::15::INSTR PXI device number 15 on bus 0 with implied function 0.
PXI::2::BACKPLANE Backplane resource for chassis 2 on the default PXI system, which is interface 0.
PXI::CHASSIS1::SLOT3 PXI device in slot number 3 of the PXI chassis configured as chassis 1.
PXI0::2-12.1::INSTR PXI bus number 2, device 12 with function 1.
PXI0::MEMACC PXI MEMACC session. A TCP/IP device using VXI-11 or LXI located at the specified address. This uses the default LAN Device Name of inst0.
TCPIP0:: Raw TCP/IP access to port 999 at the specified IP address.
USB::0x1234::125::A22-5::INSTR A USB Test & Measurement class device with manufacturer ID 0x1234, model code 125, and serial number A22-5. This uses the device’s first available USBTMC interface. This is usually number 0.
USB::0x5678::0x33::SN999::1::RAW A raw USB nonclass device with manufacturer ID 0x5678, model code 0x33, and serial number SN999. This uses the device’s interface number 1.
visa://hostname/ASRL1::INSTR The resource ASRL1::INSTR on the specified remote system.
VXI::1::BACKPLANE Mainframe resource for chassis 1 on the default VXI system, which is interface 0.
VXI::MEMACC Board-level register access to the VXI interface.
VXI0::1::INSTR A VXI device at logical address 1 in VXI interface VXI0.
VXI0::SERVANT Servant/device-side resource for VXI interface 0.