Design Con 2015

Embedded software critical for instrument design

-September 06, 2013

Editor’s Note: David Wyban from Keithley Instruments explains how consumers’ demand for higher functionality makes
 embedded software necessary for next-generation test and measurement instrumentation.--JSL.

The demand for higher functionality in practically every consumer electronic product ─ from smartphones to tablet computers─makes testing the components that go into these products more challenging with every passing year. Therefore, because the designs of these components are evolving faster than ever, they require new testing routines to characterize and/or confirm their performance.

That often means that the test instruments used last year for characterizing the current-voltage (I‑V) characteristics of a device may lack the capabilities necessary for this year’s test challenges. One of the results of this constant change is the growing use of embedded microcontrollers/script processors and embedded software, which allow for local control of an instrument’s operation, rather than running a control program on an external PC and communicating commands to the instrument via GPIB, USB, LXI or other interface.

Embedded Microprocessors Speed Test Execution
A test script is a collection of instrument control commands and/or program statements. These program statements control script execution and provide facilities like variables, functions, branching, and loop control. Scripts are written using a scripting language, such as Lua, which allows users to create powerful, high-speed, multi-channel tests with significantly reduced development times. Test scripts can be downloaded into either volatile or nonvolatile memory of an instrument with an embedded script processor to allow the instrument to control itself, independent of the system host controller. This can free up the system controller to interface with other instruments in the rack more frequently, thereby increasing the overall system throughput.

Recently, some test script processors have begun making it possible to embed complete test programs within the instrument itself and then execute them. This virtually eliminates all the time-consuming bus communications to and from the PC controller, dramatically improving overall test times. Figure 1 illustrates how an instrument with an embedded microcontroller functions.


Figure 1: Test script processor technology executes complete test programs from non-volatile memory.

Some instruments with an embedded script processor can even control multiple instruments from a single master by connecting to each other via a high-speed trigger synchronization/inter-unit communication bus. A test script runs on the embedded script processor on the master instrument and controls any slave unit(s): one script program controls both the master and any connected slaves. This type of master/slave operation is much faster than sending commands and trigger signals back and forth between the controller and the individual instruments in the test configuration over a traditional communications bus and helps reduce programming complexity. Systems based on this kind of architecture also offer test engineers superior flexibility, allowing for quick and easy system re-configuration as test requirements change as new versions of components are created.

Embedded Software Enables “Plug-and-Play” Characterization
Embedding test software in the instrument itself allows users to start making measurements far sooner than they could if they had to write and debug a test program to run on a PC or even a test script. For example, TSP® Express, Keithley’s embedded Java-based test software for Series 2600B SourceMeter® SMU instruments, allows users to begin characterizing new devices almost immediately, with no need for software installation or programming, enabling I-V characterization through any browser, on any computer, from anywhere in the world. Test engineers can connect these instruments to the internet via a LAN cable, open a browser, type in the instrument’s IP address, and begin testing. The resulting data can be downloaded to a spreadsheet program such as Excel for further analysis and formatting, or for inclusion in other documents or presentations.

The combination of embedded script processors and embedded software in a single test instrument simplifies system integration, which can help test system builders and users keep up with fast-changing device test challenges. (For a demonstration, see my online video on Plug & Play test software. )

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