6288030.pdf

BY AUTHOR’S NAME • TITLE

abbreviations go by on a screen.

Logic analyzers traditionally fit into

large desktop enclosures, but several man-

ufacturers now offer small, “pocket-sized”

logic analyzers that rely on a host PC for

display, control, and storage capabilities.

We tested seven of these instruments and

report our results for you here. Tests in-

volved the use of a standard microcon-

troller-development kit and simple pro-

grams written in C.

There are several areas of concern to

keep in mind while evaluating these or

similar instruments in your lab.

Connections: Several analyzers come

with small grabber clips. Connecting to

eight signals on a row of pins spaced at

0.10-in. intervals provides a challenge.

Other instruments provide a choice of

female contacts that push onto 0.025-in. 2

pins.

Triggers: All logic analyzers in this

review provide triggering, because that’s

what logic analysis is all about: You want

to see what happens when an event occurs.

Unfortunately, some analyzers provide

triggers that act on only logic levels and,

in one case, could set up a trigger based on

only four signals. These days, analyzers

need level and edge triggering, and some

engineers need sequential triggers, such as

“trigger if Condition A follows Condition

B.” Know your triggering requirements, so

that a purchase doesn’t disappoint you.

Cursors: These movable marks that

locate signal features prove troublesome

in many displays. Software should give

you complete control over cursors and

should show you where the cursors are,

how to control them, and the time mark

they represent in a display. The ability to

calculate the time between sets of cursors

makes them particularly valuable. A dis-

play should not “lose” cursors so that you

have to go and look for them.

And last, you cannot have a good logic

analyzer without solid documentation.

BY JON TITUS • CONTRIBUTING EDITOR

HANDS-ON REVIEW:

ANALYZERS REVEAL

DIGITAL SECRETS

ogic analyzers capture digital signals and display state

information, timing information, or both. When test-

ing or troubleshooting electronic equipment, engi-

neers use these instruments to extract microcontroller

timing information, monitor sequences of digital

events, watch instructions go to and from a micro-

processor, and so on. Wherever you need to monitor sequences of

bits and bytes, you’ll find that a logic analyzer fills the bill. In

addition to watching the usual flow of signals on parallel lines,

some logic analyzers can decode I 2 C, SPI, CAN (controller-area-

network), and other serial protocols. And, if you plan to debug

an embedded computer, you also can decode instructions so that

you can watch the flow of a program, step by step, as op-code

MORE AT EDN.COM

For details on our testing tools and

procedures, see the sidebar “How we

ran the tests” at www.edn.com/

051205df1. At this link, you’ll also find

the code we used for tests 1 and 2,

which you will read about in the follow-

ing pages, as well as a table summariz-

ing each of the seven logic analyzers.

DECEMBER 5, 2005 | EDN 67

PC-BASED LOGIC ANALYZERS CAN REVEAL MUCH ABOUT DIGITAL

SIGNALS. HERE’S THE LOWDOWN ON SEVEN MODELS WE TESTED.

HANDS-ON REVIEW

BitScope BS-50 Pocket Analyzer

Price: $345

www.bitscope.com

or for a sequence of events that trigger

acquisition of signals.

We ran the Test 1 code on the Rabbit

board and set triggering for a logic-one on

D0 and a logic-zero on D1. The display

seems upside-down, with D7 at the top

and D0 at the bottom. The software pro-

vides no way to change the color or to

name the traces.

To acquire data, users click “repeat” to

continuously acquire and display data

whenever the analyzer “sees” the trigger

condition and is not busy acquiring data.

A click on a trace, though, initiates a one-

shot capture. The timebase controls let

users select a timebase of 25 nsec to 200

This small module provides logic-analyz-

er and DSO (digital-storage-oscillo-

scope) functions, and it includes a single-

channel AWG (arbitrary waveform gen-

erator). Setup went smoothly, although

engineers may find it easier to work with

a 26-pin header than with individual

wires. The color-coded wires that accom-

pany the analyzer provide a grabber on

one end and a 0.025-in. female connec-

tor on the other. The grabbers crowd the

I/O pins on our test board, but they fit

snuggly and held in place during testing.

The BitScope DSO 1.2 software starts

easily, but it takes a moment to realize

that you have to click the power button

to “start” the instrument. The software’s

initial screen looks like a DSO, but a click

on the logic button on the right-hand

menu produces the eight logic signals the

module can acquire. When the software

changes to logic-analyzer mode, the

upper-left trigger area displays each logic

signal and an associated button that lets

you select a logic-zero, logic-one, or don’t-

care condition for triggering. The soft-

ware does not provide for edge triggering

. The

display shows a time-delay value, the

timebase value, and the sample rate. We

chose a 1-

play shows the location of the cursor rel-

ative to your current view of the acquired

data. And you can’t click within a display

of data to retrieve the x cursor from a dis-

tant or forgotten position; you must hunt

for it.

We performed the BIOS interrupt-tim-

ing measurements on the Pocket Ana-

lyzer’s data and calculated an average

period of 488

sec. EDN

zoom

factor, and the data generated by Test 1

appeared in the display area. Although

the display triggers properly, we could not

relate the TD value to anything we had

set or could control.

The display provides an x-axis cursor

and a display of the x cursor’s time rela-

tive to the trigger. But good luck if you

can’t remember where you placed the cur-

sor the last time you used it. No subdis-

sec timebase and a 1

Bottom line: Before you use this

analyzer, the manufacturer should

upgrade its software. The inability to

easily move a timing cursor and the

lack of signal-name assignments

and color codes make the instrument

difficult to use. Because the manual

concentrates on DSO measure-

ments, logic-analyzer operations get

scant coverage.

Cwav USBee ZX Test Pod

Price: $895

www.usbee.com

The display window shows all eight

color-coded signals, which users can

name as they like. Four columns near the

signal names let you select sequential-trig-

ger conditions based on logic-one, logic-

zero, or don’t-care states. If you do not set

a trigger condition, the module starts to

acquire data as soon as you click on the

“acquire” button in the acquisition area.

The trigger levels prove easy to manipu-

late and the module easily acquires data

from the Test 1 and Test 2 program runs.

The display area includes two cursors,

X and O, that you can move freely

through the data. Three windows show

the time position of the cursors, as well

as the time difference between X and O.

You can set X, O, or T (the trigger con-

This module provides eight digital in-

puts, a ground line, an external trigger,

and clock lines. The built-in wires come

with female adapters that slide onto

0.025-in. 2 pins. The unit includes micro-

clips that can grab component leads.

Sampling of digital signals takes place at

nine rates from 1M to 24M samples/sec.

Because the module uses a PC’s internal

memory for storage, acquisitions can run

from 1M to 810M samples, depending

on the PC memory available. Users can

add modules to acquire data from more

than eight signals at a time. Each mod-

ule provides both 5 and 3.3V outputs.

dition) as the reference for time meas-

urements. Measuring the times between

the expected glitch in the data during

Test 1 provides an average time of 485

68 EDN | DECEMBER 5, 2005

sec and a zoom factor of 10 to 20

sec from eight consecutive measure-

ments. The cursors and the display con-

trols are easy to use. An additional meas-

urement, Insta-measure, lets you select

width, frequency, period, or byte. Select

one of these measurements, and it appears

next to the cursor as you move it among

the waveforms.

Because the module comes with what

looks like an external trigger input, we

decided to use it to trigger the logic ana-

lyzer. Although the USBee ZX software

includes help files that exist as video seg-

ments, the triggering options that the

video segment describes do not match the

latest version of the logic-analyzer soft-

ware. A printed manual would help.

How hard can it be to configure a sim-

ple trigger input line? We set up condi-

tions to try and clicked on the “acquire”

button. A blue “waiting-for-trigger” indi-

cator flashed for longer than appropriate

for the signal we had selected as the trig-

ger source. So, we clicked on the “stop”

button to abort the run. That action sent

the software into the “not-responding”

condition, and, in this state, the Windows

task manager could not shut down the

program. To double-check the operation,

we tried similar external trigger actions,

and all locked up the program. If you

leave it long enough, the program even-

tually shuts down.

Tim Harvey at USBee at first re-

marked that we had uncovered an un-

known bug in the software, which

should otherwise let users gracefully

“back out” of a condition in which the

software waits for a trigger and a clock

signal. He later explained that we prob-

ably needed to upgrade our USB-port

drivers because early drivers had a prob-

lem that prevented certain timing oper-

ations from working properly. EDN

Bottom line: The logic-analyzer func-

tions work well, and the ability to cas-

cade USBee ZX modules in parallel

makes the logic-analyzer functions

useful. This unit will appeal to design-

ers who develop small embedded sys-

tems and who need basic logic-analyz-

er functions.

Dynon Instruments Elab-080

Price: $495

www.dynoninstruments.com

logic-analyzer functions, we ran Test 1 so

that we had some data to capture. Click-

ing a green arrow button in the control

window started an acquisition, but we

could see no changes in the data, and, no

matter how we adjusted the sample rate,

the display timing remained fixed.

Off to one corner, the control window

displays a group of two buttons: (DSO/

LA Zoom). Yes, the label is in parenthe-

ses. The buttons carry labels S and nS.

Clicking the buttons zooms the display

out and in, respectively, so we could see

more or less of the data. After zooming

appropriately, we could see the eight

logic-zero signals.

Clicking on the logic-analyzer tab in

the control window opens a subwindow

that lets you quickly label signals, desig-

nate a signal’s source, and change a sig-

nal’s displayed color. Changing a name

does not change the signal’s channel

number—a nice feature that makes it easy

to name signals and still know what

points they come from on a circuit. A

“buses” tab lets users group signals and dis-

play bus information in octal, binary, dec-

imal, or hex format.

A “trigger” tab lets you select an op-

tional trigger, but trigger choices appear

limited. You can select to trigger only on

patterns that involved channels 00 to

03. The trigger-setting window accepts

any binary pattern except for 00002.

The unit’s help file explains that a hard-

scope probes. We confined

investigations to the logic-analyzer por-

tion of the unit and its software. The

package includes the main instrument

box, a large plug-in power supply, and

connection leads. The leads connect to

a header that furnishes eight signal leads

and a ground for each. Labels CH1, CH2,

and so on mark the leads so that you need

not rely solely on the color-coded wires

for identification at your system under

test.

Unfortunately, the package lacks a CD-

ROM, manual, and quick-start guide.

Instead, a slip of paper asks users to visit

the Dynon Web site to download the lat-

est software. We downloaded the software

onto a USB memory stick and moved it

to an isolated lab PC. The setup went

well, and the installed software displayed

windows for the logic-analyzer wave-

forms, oscilloscope signals, and spectrum

display.

Controls make it easy to set a sample

rate (1 kHz to 100 MHz in one, two, or

five steps) and a sample size (1k sample

to 32k samples in 2n steps). To test the

ware limitation causes that problem.

The analyzer may accept an external

trigger signal on a separate pin, but

nothing in the trigger window provides

a clue about using this input line. Sev-

eral trigger combinations work as you

would expect. When you remove the

check mark from the enable-trigger

option, the analyzer simply acquires data

as soon as you click on the green arrow

button.

The display provides two timing cur-

sors, A and B, that have little value.

The Elab-080 software displays numer-

ic-timing information in a separate win-

dow so that you can view state changes

as they relate to sample times (timing

analysis). Unfortunately, the display

simultaneously shows only 19 time-

stamped samples, and you cannot ex-

pand the size of this window.

The lack of a manual and a quick-start

DECEMBER 5, 2005 | EDN 69

The Dynon Instruments Elab-080 pro-

vides a 16-channel logic analyzer, a two-

channel digital oscilloscope, and a one-

channel arbitrary- waveform generator.

The package includes two 60-MHz

/10

HANDS-ON REVIEW

guide troubles us. A user new to logic ana-

lyzers and other PC-based instruments

needs some hand-holding that this prod-

uct doesn’t provide. The software comes

with a help file that includes some expla-

nations of controls and displays, but the

information about the timing cursors, for

example, simply explains that they exist

and that a user can move them. EDN

gering options and cursor-timing in-

formation, however, limits the use of

this instrument as a logic analyzer.

When compared with the other in-

struments, this one fails to deliver the

performance you should expect from

an instrument that costs almost $500.

Bottom line: The instrument provides

more functions than you would ex-

pect, which may make it attractive in

some lab situations. The lack of trig-

Link Instruments LA-2124-128K

Price: $800

www.linkinstruments.com

offers 14 1-2-5 steps from 5k samples/sec

to 100M samples/sec.) A right click on

the signal-name column lets you change

the designation for each signal and its

color. Trigger setup involves clicking on

“trigger” and then on “trigger word.” You

can set up a pattern of logic levels and

don’t-care conditions (logic zero or logic

one) for a group of eight signals. You can

select a trigger or trigger-false condition,

and the software lets you establish triggers

in binary, hexadecimal, ASCII, or deci-

mal formats. The trigger menu also pro-

vides a threshold setting that ranges from

Link Instruments provides a family of

logic analyzers that operate with a PC

over either a parallel-port or a USB-port

connection. We chose the least-expen-

sive model, which uses the parallel port.

Users who have another device con-

nected through the parallel port may opt

for a USB-compatible model with a faster

sampling rate and more channels but at

higher cost. The software setup goes

quickly until Windows asks you to install

a device driver. The company’s technical-

support person claims that the driver

exists within the installed software direc-

tory (C:/la2124), not on the supplied CD-

ROM. He also suggests downloading Ver-

sion 1.34 of the software.

Hardware setup goes easily, too, al-

though we dislike pushing individual wires

onto small pins. We’d prefer a cable con-

nected to a single header. The analyzer

comes with 30 color-coded E-Z-Hook

(www.e-z-hook.com) clips, though, so you

can attach the clips to the signal pins and

the clips to the analyzer’s wires. This

model accommodates as many as 24 logic

inputs, and it provides for an external

clock and trigger signal.

After connecting eight wires plus

ground, we ran the LA-2124 software and

set up Test 1 on the Rabbit test board. A

click on the displayed “go” button caus-

es the unit to acquire data in single, nor-

mal, or automatic mode. In single or nor-

mal mode, the analyzer waits for a trigger

and then acquires data. Normal operation

acquires a new buffer’s worth of data after

each trigger. Automatic mode acquires

data regardless of the trigger settings.

After adjusting the sample rate with a

plus and a minus button, we could see use-

ful test results. (The sample-rate control

2.80V. The default is 1.4V.

Set the relative size of the pretrigger and

post-trigger record lengths by dragging the

red trigger cursor along a time line that

represents the data-buffer’s depth. A small

box, or timing window, on this line rep-

resents the amount of information in the

display window below it. Cursors A

through D let you mark positions in the

data, and you can use cursors A and B to

measure the time between two points or

between each cursor and the trigger point.

The BIOS interrupt period is 488

a processor so you can examine instruc-

tions and data as they flow over buses in

a system. By adding extra columns of data

in different formats, you can examine

state information as binary and hexadec-

imal codes.

The software neither “collapses” a

group of signals into a bus nor displays a

hex, decimal, or other code for bused sig-

nals. But the state window provides some

of those capabilities. The state window

and the timing window do not link to

each other, although you can coordinate

cursors between them. You can insert a

“spacer”—essentially, a colored bar—

between groups of signals to separate

them from other signals. EDN

sec.

The cursors are easy to use and helpful.

You can track a cursor by its color, and a

check mark in a small display also lets you

know which cursor you have under con-

trol of the mouse. Cursor movements

involve “grabbing” one with the mouse,

or you can select one in the upper-left cur-

sor box and use six buttons to move it left

or right in time increments. The cursors

also appear along the time line, so you

always know their locations. Menu

choices let you quickly move the cursors

into the display area. The display pro-

duces the state data as hexadecimal, bina-

ry, decimal, or ASCII characters. You can

assign your own values to the display and

can include a translation table. The trans-

lation table lets you establish op-codes for

Bottom line: There’s a lot to like

about this instrument. The built-in

ability to handle 24 inputs as well as

an external clock and trigger makes

this instrument useful for embed-

ded-system designers. The ability to

add modules makes it easy to ex-

pand digital inputs. The menus are

generally intuitive, although we had

to ask tech support how to remove a

spacer. If the analyzer lacks any-

thing, it’s the ability to set up edges

as triggers and to establish sequen-

tial trigger conditions. We give this

unit high marks, and, in this case,

the lack of a printed manual causes

no problems.

70 EDN | DECEMBER 5, 2005

1.15V to

HANDS-ON REVIEW

NCI GoLogic-72 System

Price: from $4300

www.nci-usa.com

more than basic triggering, plan to spend

time learning about the various triggering

modes by experimenting with them. To

start acquisition of data for Test 1, we

wanted to trigger on a falling edge on sig-

nal A0. Clicking on the setup tab lets you

select a simple edge trigger, but we could-

n’t figure out how to select the A0 signal.

After we gave up and switched back to

the waveforms display, we noticed small,

gray squares associated with each signal.

Clicking on these squares lets you select

without going back to the setup menu.

The logic-analyzer software also pro-

vides a sample-by-sample numeric display

of information. So, the software lets you

monitor data value on a bus rather than

waveforms. You can still use the cursors to

mark values and determine the time

between them. If you have a waveform

and a numeric display open simultane-

ously, moving around in one display also

moves your view in the other. Thus, you

can easily track logic levels and numeric

data. The logic analyzer detects the anom-

aly that the Rabbit board’s BIOS causes

and measures the time over 10 occur-

rences over a period of 489

The GoLogic-72 System provides for as

many as 72 digital inputs and eight clock

inputs, which makes it a powerful tool for

testing and debugging embedded systems

that require monitoring of several buses,

I/O ports, and control signals. The unit

comes with all 72 connections, split into

two groups. Each group of eight labeled

connections passes through a small harness

that makes it easy to handle them all

simultaneously. This feature simplifies

setup when attaching connections to a

board. The wires each furnish a female

connector that pushes onto 0.025-in. 2

pins, which is how we used the logic ana-

lyzer. NCI also provides micro-grippers ($4

each) and nano-grippers ($7 each) to con-

nect with small and tiny component leads.

The GoLogic system comes with a CD-

ROM, and it takes little time to install the

software and get it running. The module

connects to a supplied power cube and to

a PC through a USB cable. The compre-

hensive manual provides basic informa-

tion on how the analyzer works and then

goes into details about sampling, clock-

ing, state analysis, timing analysis, and

triggering. Unfortunately, the manual

looks formidable, and no quick-start tuto-

rial exists to take you on a tour through

the many options and menus.

Lacking such a tutorial, we plunged in

and connected the lines labeled A0 to A7

plus two ground lines to the test board. A

setup menu lets you select a sample rate,

memory depth, and the type of sampling.

Nine options for sampling include I 2 C

and SPI modes for troubleshooting seri-

al communications in embedded systems.

Next, you select the channel groups,

which show the wire color codes and indi-

cate signal activity on lines A0 to A7. The

threshold for the signals is 1.58V, but you

can reset it for ECL signals or adjust it from

sec. The dis-

play also shows two “glitches” on the A7

and A6 lines where the other signals

change state. The period of these glitch-

es always equals the sampling period: 8

nsec at 125M samples/sec and 20 nsec at

50 MHz. So, it seems unlikely that the

glitches existed; they do not expand and

shrink in sync with the sampling clock.

But glitches might arise from simultane-

ously switching so many loads (the LEDs).

Do the glitches you observe with the

logic analyzer but not with the scope

exist, or does the logic analyzer “see”

something that doesn’t exist? You’d need

a storage scope to tell. EDN

a rising, falling, rising-or-falling, or

unused triggering attribute. You can scan

through the trigger settings you used pre-

viously, which makes it easy to keep sev-

eral settings at hand for complex tests.

Displays that include at least one chan-

nel (signal) include three pairs of cursors

you can move with the left or the right

mouse button to measure times between

events. Luckily, you need not drag a cur-

sor from place to place. Clicking on an

area of the waveform display moves the

selected cursor to the clicked-on position.

The cursor notations need some enhance-

ments, though. It is difficult to tell which

set of cursors is active and which mouse

button controls a given cursor.

Moving on to the binary-count test

(Test 2) lets you set up a pattern trigger for

FF (hexadecimal) and set the duration of

the trigger for at least 8

sec, which put it

about in the middle of a 1-LSB level. That

trigger setup works, and the display pro-

vides the expected data. In this test, the

gray trigger squares indicate logic levels

rather than transitions. You can click on

these squares to change trigger conditions

Bottom line: Although priced much

higher than any other analyzer, the

wealth of triggering options provides

a strong justification for buying this

unit. The display options and the cur-

sors make it a solid analytical tool.

Plan to spend time learning about the

triggering modes and options.

Unfortunately, lack of time prevented

us from exercising many capabilities,

such as searching data for patterns

and triggering a storage scope and

simultaneously displaying analog and

digital data. The analyzer links with

disassemblers and displays C/C

source code so you can observe op-

code-by-op-code operation of a pro-

gram. Software add-ins that provide

these functions cost extra.

5.27V for other logic families.

We downloaded Test 1 to the Rabbit

test board to make information available

to the analyzer. If you need to perform

72 EDN | DECEMBER 5, 2005

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