(^42) DESIGN WORLD — EE NETWORK 6 • 2019 eeworldonline.com | designworldonline.com
TEST & MEASUREMENT HANDBOOK
B&K Precision Corp.
http://www.bkprecision.com
The initial setup of a USBTMC instrument only requires VISA
software installation. NI-VISA is widely used software provided
by National Instruments Corp. that implements this architecture.
This package also includes the Measurement & Automation
Explorer (NI-MAX) which allows for auto-detection and remote
communication with test instruments from a PC.
Once NI-VISA is installed on the computer, the connection and
powering-up of any USBTMC device would trigger the automatic
installation of the correct instrument drivers. Check the device
manager on a Windows system to verify a resource called “USB
Test and Measurement Device” is available. A common problem
faced by Windows users is the automatic download of incorrect
drivers as a result of not first downloading and installing VISA
software before connecting the instrument to the computer; be
sure that the instrument communication setting is set to USBTMC.
Moving forward, test and measurement manufacturers will
continue to incorporate USB and USBTMC as a standard interface.
GPIB connectivity is now commonly offered as a more expensive
option and is reserved for larger test systems. For simple benchtop
applications, the combination of plug-and-play connectivity, low
cost, and GPIB emulation combine to make USBTMC a more widely
used option for test and measurement equipment.
In that regard, B&K Precision moderates a github repository
resource where users can find code samples in a variety of
languages, LabVIEW drivers, and USBTMC utilities for Linux
environments. Users can also find a full step-by-step tutorial video
on installing the required software and setting up an instrument
for remote communication using USBTMC on the B&K Precision
YouTube page.
General comm model for USBTMC interface
device
USBTMC
interface
Host
Control endpoint (required)
Bulk-OUT endpoint (required)
Bulk-IN endpoint (required)
Interrupt-IN endpoint (optional, subclass may require)
The general communication model for a USBTMC
interface. USBTMC client software must be able to
support the endpoints shown. A USBTMC subclass
specification may make some of the endpoints
optional. The control endpoint is required by the
USB 2.0 spec. The Bulk-OUT endpoint is required
and is used to provide a high-performance,
guaranteed delivery data path from the Host to the
device. The Host must use the Bulk-OUT endpoint
to send USBTMC command messages to the
device, and the device must process the USBTMC
command messages in the order they are received.
The Host must also use the Bulk-OUT endpoint to
set up all transfers on the Bulk-IN endpoint. The
Bulk-IN endpoint is required and is used to provide
a high-performance, guaranteed delivery data path
from the device to the Host. The Host must use
the Bulk-IN endpoint to receive USBTMC response
messages from the device. The Interrupt-IN
endpoint is used by the device to send notifications
to the Host. A USBTMC subclass specification may
require an Interrupt-IN endpoint. If the interface
descriptor has bInterfaceProtocol = 0, then no
subclass specification applies and the USBTMC
interface is not required to have an Interrupt-IN
endpoint. The Host USBTMC driver may optionally
support additional endpoints if the endpoints are
required by a USBTMC subclass specification.
B&K — Test and Measurement HB 06-19.indd 42 6/10/19 9:33 AM
amelia
(Amelia)
#1