Text preview for : LA.pdf part of Tektronix LA Tektronix publikacje LA.pdf
Back to : LA.pdf | Home
The XYZs of Logic Analyzers
L o g i c
A n a l y z e r s
The XYZs of Logic Analyzers
Primer
The XYZs of Logic Analyzers
Contents
Introduction . . . . . . . . . . . . . . ........................................ . . . . 2
Where It All Began . . . . . . . ......................................... . . . . 2
The Digital Oscilloscope . . ......................................... . . . . 2
The Logic Analyzer. . . . . . . ......................................... . . . . 3
Logic Analyzer Architecture and Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Connect to the System Under Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Set Up Clock Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Set Up Triggering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Simultaneous State and Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Real-time Acquisition Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Analysis and Display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Waveform Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Integrated Analog-digital Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Listing Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
www.tektronix.com/logic_analyzers 1
The XYZs of Logic Analyzers
Primer
Introduction
Like so many electronic test and measurement tools, a logic analyzer
is a solution to a particular class of problems. It is a versatile tool
that can help you with digital hardware debug, design verification
and embedded software debug. The logic analyzer is an indispensa-
ble tool for engineers who design digital circuits.
Logic analyzers are used for digital measurements involving numer-
ous signals or challenging trigger requirements. In this document,
you will learn about logic analyzers and how they work.
In this introduction to logic analyzers, we will first look at the digital
oscilloscope and the resulting evolution of the logic analyzer. Then
you will be shown what comprises a basic logic analyzer. With this
basic knowledge you'll then learn what capabilities of a logic ana-
lyzer are important and why they play a major part in choosing the
correct tool for your particular application.
Figure 1. The oscilloscope reveals the details of signal amplitude,
rise time, and other analog characteristics.
Where It All Began
Logic analyzers evolved about the same time that the earliest commercial A look at the waveform in Figure 1 illustrates the oscilloscope's
microprocessors came to market. Engineers designing systems based strengths. The waveform, though taken from a digital circuit, reveals
on these new devices soon discovered that debugging microprocessor the analog characteristics of the signal, all of which can have an
designs required more inputs than oscilloscopes could offer. effect on the signal's ability to perform its function. Here, the oscil-
Logic analyzers, with their multiple inputs, solved this problem. loscope has captured details revealing ringing, overshoot, rolloff in
These instruments have steadily increased both their acquisition the rising edge, and other aberrations appearing periodically.
rates and channel counts to keep pace with rapid advancements in With the oscilloscope's built-in tools such as cursors and automated
digital technology. The logic analyzer is a key tool for the develop- measurements, it's easy to track down the signal integrity problems
ment of digital systems. that can impact your design. In addition, timing measurements such
There are similarities and differences between oscilloscopes and as propagation delay and setup-and-hold time are natural candidates
logic analyzers. To better understand how the two instruments for an oscilloscope. And of course, there are many purely analog
address their respective applications, it's useful to take a compara- signals