GPIB: Challenges and opportunities by fdjerue7eeu


									GPIB: Challenges and opportunities
IEEE 488 standard has a well-known name, called GPIB (general-purpose interface
bus). This is a very popular interface for connecting test and measurement instruments
and computer, to form an ATE (automatic test equipment). GPIB originally developed
by HP, and in 1978 was recognized as an IEEE standard. Since then, IEEE in 1978
and 1987 respectively, issued a definition of GPIB hardware specifications (including
the electrical parameters, mechanical parameters and parameters based on the
agreement) and IEEE 488.1 standards and definitions related to software specification,
IEEE 488.2 standard. For decades, GPIB instrument makers by widely accepted and
used. It can be said, GPIB is currently in the computer and test and measurement
equipment to connect the interface to use the most.

GPIB challenge

      PCI I / O bus of the revolutionary changes (such as higher data throughput,
smaller footprint) to promote the traditional ISA bus and PCI bus standard is more
mature popularity. The bus standard in the transmission speed is far more than RS-232.
The most outstanding is the USB and LAN interfaces, which proved higher than other
interfaces, faster, more comprehensive performance. Because of their cost-effective
and convenient connections, so the current PC machines are equipped with two
interfaces. Meanwhile, countless traditional GPIB device experienced 30 years of
improvement and development of a wide range of after, and now also support hot
swap features and remote access to not lag behind the test engineers more familiar
with IP-based instruments. Because the GPIB of these innovations, updates, and faster
I / O interface (such as USB or LAN) be very difficult to replace GPIB position in
ATE industry.

      Recognizing the GPIB position in this market stable, mainstream instrument
manufacturers developed by the GPIB to USB or LAN bridging communication
protocol. This fully protects the user interface to GPIB instruments on past
investments, but also enables users to benefit from the flexibility of USB and LAN
interfaces, and high data throughput advantage. Bridging communication protocol to
GPIB to USB / LAN adapter, GPIB-LAN gateways and converters in the form of
realization. Bridging communication protocol and related technology trends show,
GPIB interfaces will have a place.

     From the hardware point of view, GPIB with USB / LAN interface
interoperability is not required in the expansion slot and then install ISA / GPIB card
and realize a more rapid integration and maintenance easier, reducing test cost and
complexity .

     From the software point of view, GPIB and USB / LAN combination of the same
great advantage. Because most of the mainstream operating system can monitor the
status of LAN or USB port, so any new equipment can be connected to automatically
detect and identify. Such as the Agilent I / O Library Expert of the class of highly
integrated environment can automatically recognize connected instruments and assign
a dedicated software resources, so no need to connect devices that have manual search,
identification and initialization.

GPIB Application Tips

    To achieve a set of ATE in the beginning before the user first examination to
answer the following questions / issues:

     You want to connect the instrument of choice is what kind of physical interface:
     Software requirements, specifications, capabilities and performance?
     According to the selected software application, you will use that software
development environment to control the apparatus and its communication?
    ?Suppose the user decided to use GPIB as the instrument control interface, then
the next step is to communicate with instruments to determine the I / O package.
These I / O software tools is considered in the design of integrated applications to
connect the instrument software layer between the physical interface. Create
automated test applications in two ways: the use of local driver API or through the
Advanced Instrument Driver.

                                               ?Figure 1: GPIB interface card in the
development process and tools.

     The first method involves local driver API conventions. The API is usually most
of the adapters manufacturers agreed to provide ANSI C function. Recommended that
the need for complex instrument control and want to achieve maximum system
throughput for users with a SCPI command characters driver API.

     As for the wish to avoid writing complex instructions instrument users, VISA or
IVICOM advanced instruments such as the driver is the ideal solution. VISA is a
software interface for the computer and communications equipment to provide the
standard measurement of input and output functions.

     The advanced instruments for all types of libraries can be connected to provide a
transparent interface to software compatibility, while providing the functions are
mostly used by the device interface with the phase independence. Whether you are
preparing via RS-232, GPIB, USB or LAN interface, access to measurement
instruments, changing the communication bus type, not high-level instrument drivers
modify the software code will give you additional burden. Finally, the senior
instrument driver allows you to have more time to focus on software development, but
also allow users to program the re-integration in the future with greater scalability.

     Determine the software I / O layer, the next step will be to choose the most
appropriate ADE (application development environment). ADE combination with
software tools package is critical, will directly affect the overall application
development costs and completion time. Therefore, the price of the software and the
time required for study or training must be carefully considered. Meanwhile, the
programmer may also need to consider software development kits to accelerate test
system development. Software development in two ways: graphical development and
text-based development.

     At present, the line test and measurement engineering, graphical programming
environment there are many. Among the most popular is Agilent's VEE and
NI's LabVIEW, both have friendly GUI and programming methods, which
are suitable for novice programmers. Easy to use graphical programming environment
allows users to quickly create a prototype test system, and effectively deal with
several parallel data flow between activities. Graphical programming environment to
support the direct way than the procedure used to create a simple text program. In
addition, graphical programming environment, programmers need to know the
complex syntax, because it can help programmers more easily to learn and share
predefined code.

     Text of ADE in the development of large-scale programming is suitable for
applications and increase system throughput use. However, this programming
approach requires programmers to have enough experience. Fortunately, graphical
programming and text-based programming, the difference between run-time
performance has recently been reduced.

     Table 1: Comparison table of different standards in key specification differences.
Theoretical bandwidth and the actual flow of the bus is not the same, it depends on
the host computer's processing speed, above the equipment installed, and
sudden changes in the data block size.

GPIB interface compared with other

      The instrument manufacturers and users, fast and reliable connection is most
important. As the business desktop and notebook computers increasing the
performance, PC and communication between devices based on evolution have
emerged. While GPIB remains the de facto standard for connecting devices, PCI bus
is still the standard industrial control and measurement I / O interfaces, USB and
Ethernet, but a new generation of instrument control in the field began to break into.
Therefore, it is necessary to evaluate and compare these interface standards. The
following table compares the different standards in key specification differences.
Theoretical bandwidth and throughput of the bus is not the same, it depends on the
host computer's processor speed, installed equipment, and sudden changes
in the data block size.

     ATE in the structures, select I / O interface is the first step. You can use pure
GPIB interface with traditional instruments, you can use with a LAN or USB interface
when the new equipment. The combination of GPIB and USB / LAN is a
comprehensive program to meet various requirements. Mentioned earlier, if the
choice of equipment support and other high-VISA driver, then you can appreciate the
high-level driver to create hybrid flexible high-performance test systems advantages.

GPIB controller with FPGA Implementation

     GPIB GPIB bus controller is a key component, it is usually an ASIC. Production
of such small components supplier, so based on the GPIB ASIC expensive. Although
the component manufacturers are convinced based on the GPIB ASIC than
FPGA-GPIB better performance, but its high cost does not the latter, especially in the
prototyping or small-scale production.
With the development of EDA tools, FPGA provides an alternative to expensive ASIC
to achieve GPIB option. Meanwhile, as more and more FPGA standards emerge, and
proven IP cores can be easily obtained through the Internet, has begun to be the GPIB
protocol embedded itself in FPGA, for test and measurement applications that provide
a very promising development opportunities.

     Previous paper can be seen, GPIB, as a reliable I / O interface, the instrument
will still continue to use large number of active duty. Meanwhile, GPIB also provides
a convenient way of managing complex hardware handshake. However, the decisive
time to market forces the GPIB interface hardware designers and equipment
manufacturers to release products as early as possible. The careful selection of the
main controller and the communication protocol between the remote device, and fully
understand the signals GPIB, time to market pressure can be brought immediate relief.
The sooner these factors are met, the faster product development.

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