Scopes Bring Simplicity To Embedded Design Debug

Dec. 3, 2007
two or four channels. Subsequently, you can search, pan, and zoom the waveforms for closer inspection. It lets you identify glitches faster and examine the details of any signal by scrolling through the captured records. This works on th

Most test-equipment manufacturers live on the leading edge of electronics. Their advanced instruments give engineers the tools to develop the latest, limit-pushing circuits and systems, because “you can’t design it if you can’t test it.”

Today’s most advanced instruments solve measurement problems at higher frequencies and faster data speeds, and they include much more sophisticated automated testing features in software. Now, these faster-sampling-rate, widerbandwidth, software-based features are finding their way into more general-purpose bench instruments used on not-soleading- edge designs.

Armed with such specs and features, these bench instruments make more common measurements a snap despite the complexity. There’s no better example of this than Tektronix’s MSO4000 series oscilloscopes.

The MSO4000 mixed-signal oscilloscope is a small but full-featured bench scope that generates quick results for complex designs (Fig. 1). This scope targets engineers who design, test, and debug embedded controller products with multiple serial interfaces, as well as related digital circuitry.

The MSO4000 includes an impressive digital signal test and analysis feature that will almost make you believe there’s no need for a logic analyzer. Though it doesn’t contain a fullfeatured logic analyzer, the MSO4000 provides 16 logic channels in addition to a standard two or four analog channels, providing more than enough inputs to test nearly anything you’re working on.

Virtually all of today’s electronic products contain at least one embedded controller. As a result, most engineers end up spending lots of time testing and debugging the microcontroller and anything tied to it, such as the analog-todigital converter. And, a standard oscilloscope almost always comes up short in embedded debugging because of the limited number of signals it can display simultaneously.

These days, the most crucial need for designers is to look at the 8-bit data bus or the 16-bit address bus. Viewing an FPGA’s inputs and/or outputs is another common challenge. A logic analyzer is the answer, but fewer labs have these expensive and complex devices. Often, they’re simply overkill for the task at hand.

This is where the MSO4000 scopes step in. They incorporate 16 digital inputs and can display all of the signals on screen at the same time (as well as up to four analog signals). This feature alone makes the scope a more versatile instrument for any lab.

There are four versions of the MSO4000. The MSO4034 and MSO4032 have a 350-MHz bandwidth and a 2.5-Gbit/s sampling rate. The MSO4054 features a 500-MHz bandwidth with 2.5-Gbit/s sampling rate. The high-end model, which I tested, is the MSO4104. It delivers a 1-GHz bandwidth with a 5-Mbit/s sampling rate. Those rates apply to all channels, and all channels have a maximum record length of 10 Msamples.

All of the scopes possess four analog channels, except for the MSO4032, which has two. Also, each scope contains 16 digital input channels, with each channel featuring a timing resolution of 60.6 ps (16.5 Gsamples/s). Because most modern microcontroller clocks push or exceed 100 MHz, you need all of the resolution you can get to resolve critical timing issues.

The userfriendly screen on this scope measures 10.4 in. in an XGA format. Additionally, you can easily see all 20 channels clearly at one time or configure the number of analog and digital channels to fit your situation. The digital signals are displayed with green high, blue low, and white rise/fall, making them easier than ever to interpret.

Another key feature is the Wave Inspector, which allows you to capture up to 10 million samples on each of the two or four channels. Subsequently, you can search, pan, and zoom the waveforms for closer inspection. It lets you identify glitches faster and examine the details of any signal by scrolling through the captured records. This works on the digital channels as well.

Also, there’s the ability to display bus data as well as trigger and search on specific data values. You can create up to four parallel buses. Then, by specifying which channels are the clock and data lines, you can assemble a parallel bus display that automatically decodes the bus content. You can even trigger on bus data values.

There’s optional support for I2C, RS- 232, SPI, and CAN serial buses, too. Almost all embedded designs use at least one of these serial buses. With the MSO4104, you can capture, decode, trigger on, and search for specific codes. The hex values of words are displayed along with the pulses.

This feature alone speeds up embedded troubleshooting measurably. And again, you can trigger on specific data values. Moreover, you can view the decoded parallel or serial bus data in a listing format. In this format, specific codes or data values are more easily identified.

The scopes come with a variety of analog probes that fit the bandwidth. The digital probe is unique in that it’s designed as two groups of eight probe lines that are color-coded (Fig. 2). Those color codes are duplicated on the screen to help you identify the line.

As mentioned before, I recently tested an MSO4104 and came away very impressed. Having used many different scopes over the years and spent hours debugging embedded designs, I can personally attest to how the scope simplifies tasks. The optional serial-bus testing features are worth every penny and will more than pay for themselves in reduced troubleshooting time.

Prices for these scopes range from $8700 for the MSO4032 to $17,200 for the MSO4104. The digital probe set is included with all versions. Serial test support is optional. All models are currently available.

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