USBee DX Mixed Signal Oscilloscope, Logic Analyzer and Bus Analyzer
This section details the operation of the Logic
Analyzer and Oscilloscope application that comes with the USBee DX, also known
as a Mixed Signal Oscilloscope, or MSO.
Below you see the application screen after startup.
The USBee DX Mixed Signal Oscilloscope functions as
a standard Digital Storage Oscilloscope combined with a Digital Logic Analyzer,
which is a tool used to measure and display analog and digital signals in a
graphical format. It displays what the
analog and digital input signals do over time.
The digital and analog samples are taken at the same time and can be
used to debug mixed signal systems.
The USBee DX Logic Analyzer / Oscilloscope application also includes embedded bus decoders and the PacketPresenter which extracts bus data packets from the logic analyzer traces and displays them in an easy to interpret format for faster debugging.
Mixed Signal Oscilloscope/Logic Analyzer
Specifications
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Analog
Channels
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2
|
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Maximum
Analog Sample Rate [1]
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24 Msps
|
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Analog
Bandwidth
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40 MHz
|
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Input
Impedance
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1M Ohm/30 pF
|
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Analog Input Voltage Range
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-10V to +10V
|
|
Analog
Sensitivity
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78mV
|
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Analog
Resolution
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256 steps
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Channel
Buffer Depth [2]
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>200k Samples
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Volts
per Division Settings
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100mV to 5V in 6 steps
|
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Time
per Division Settings
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100ns to 2s in 23 steps
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Trigger
Modes
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Auto, Normal,
Analog and Digital Triggers
|
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Analog
Trigger Voltage
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Between -10V and +10V
|
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Cursors
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2 Time and 2 Voltage
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Voltage
Display Offset
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Up to maximum inputs
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Time
Display Offset
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Up to available buffer depth
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Trigger
Position Setting
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10% to 90%
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|
Measurements
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Min, Max
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Digital
Channels
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16
|
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Maximum
Digital Sample Rate [1]
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24 Msps
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Internal
Clocking
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Yes
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External
Clocking
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Yes – through Parallel Decoder
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|
Digital
Trigger Levels
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4
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Digital
Trigger Qualifiers
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Rising Edge, Falling Edge, High,Low
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|
Trigger
Prestore
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Yes
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Trigger
Poststore
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Yes
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Sample
Clock Output
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Yes
|
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Maximum
Digital Input Voltage
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+5.5V
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|
Digital
Input Low Level
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< 0.8V
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Digital
Input High Level
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> 2.0V
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[1] Maximum sample rate depends
on your PC hardware CPU speed, USB 2.0 bus utilization and number of channels
selected.
For the fastest possible sample
rates, follow these simple steps:
- Disconnect all other USB devices
not needed from the PC
- Do not run other applications
while capturing or generating samples.
[2] Maximum buffer size depends
on your PC available RAM at the time the application is started. Each
sample requires 4 bytes of RAM (16 bits for the 16 digital lines and 8 bits each
for the 2 analog channels)
Features
Setup Configuration
The MSO can capture 16 channels of digital and 2
channels of analog at the same time. All
of the captured data is streamed over the USB bus to your PC to be stored in
the RAM of the PC. In order to optimize
the sample bandwidth you can choose to see only the channels of interest to
you.
The configurations available are as follows:
|
Analog Channels
|
Digital Channels
|
Max Sample Rate
|
|
0
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8
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24 Msps
|
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0
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16
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12 Msps
|
|
1
|
0
|
24 Msps
|
|
1
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8
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12 Msps
|
|
1
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16
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6 Msps
|
|
2
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0
|
12 Msps
|
|
2
|
8
|
6 Msps
|
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2
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16
|
6 Msps
|
To select a configuration, click Setup on the menu and select the
configuration of your choice. Below are
examples of the application in various modes.
 
16 Digital–2
Analog Channels 8 Digital–0 Analog
Channels
 
8 Digital–1
Analog Channels 0 Digital–2 Analog
Channels
Signal Names
To change the names shown for a signal, click on
the signal name and enter a new name.
Pod Status
The MSO display shows a current USBee DX Pod Status by a red or green LED. When a USBee DX is connected to the computer,
the Green LED shows and the list box shows the available Pod ID List for all of the USBee DX’s that are connected. You can choose which one you want to
use. The others will be unaffected. If a USBee DX is not connected, the LED will
glow red and indicate that there is no pod attached.
If you run the software with no pod attached, it
will run in demonstration mode and simulate data so that you can still see how
the software functions.
Acquisition Control
The MSO captures the behavior of the digital and
analog signals and displays them as “traces” in the waveform window. The Acquisition Control section of the
display lets you choose how the traces are captured. Below is the Acquisition Control section of
the display.
When the MSO is first
started, no acquisition is taking place.
You need to press one of the acquisition buttons to capture data.
The Run button is the Run/Stop control. This Run
mode performs an infinite series of traces, one after the other. This lets you see frequent updates of what
the actual signals are doing in real time.
If you would like to stop the updating, just press the Stop button and
the updating will stop. This run mode is
great for signals that repeat over time.
The Single
button captures a single trace and stops.
This mode is good for detailed analysis of a single event, rather than
one that occurs repeatedly.
The Buffer
Size lets you select the size of the Sample Buffer that is used. For each trace, the buffer is completely filled,
and then the waveform is displayed. You
can choose buffers that will capture the information that you want to see, but
remember that the larger the buffer, the longer it will take to fill.
You can also choose the Sample Rate that you want samples taken. You can choose from 1Msps (samples per
second) to up to 24 Msps. The actual
maximum sample rate depends on your PC configuration and the number of channels
that you are using. See the table below
for maximum sample rates for a given channel setting.
Trigger Control
The Mixed Signal Oscilloscope uses a Trigger
mechanism to allow you to capture just the data that you want to see. You can use either a digital channel trigger
or an analog trigger. You can not use a
combination of analog and digital.
For an Analog
trigger, you can specify the trigger voltage level (-10V to +10V) by using
the slider on the left hand side of the analog waveform display. A red line that indicates the trigger level
will momentarily be shown as you scroll this level. A small T will also be shown on the right
hand side of the screen (in the cursors bar) that shows where this level is set
to.
For an analog trigger, the trigger position is
where the waveform crossed the Trigger Voltage
level that you have set at the specified slope.
To move the trigger voltage level, just move the slider on the left of
the waveform. To change the slope, press
the Analog Trigger Slope button.
You can also specify if you want the MSO to trigger
on a Rising or Falling Edge. The following figures show a trace captured
on each of the edges.
Analog Trigger Slope = Rising Edge
Analog Trigger Slope = Falling Edge
The Trigger position is placed where the actual
signal crosses the trigger voltage with the proper slope. The USBee DX allows for huge sample buffers,
which means that you can capture much more data than can be shown on a single
screen. Therefore you can scroll the
waveform back and forthon the
display to see what happened before or after the trigger.
For a Digital
trigger, you can specify the digital states for any of the 16 signals that
must be present on the digital lines before it will trigger. Below shows the trigger settings (to the
right of the Signal labels). This
example shows that we want to trigger on a falling edge of Signal 6, which is
represented by a high level followed by a low level. To change the level of any of the trigger
settings, just click the level button to change from don’t care to high to low.
The digital trigger condition is made up of up to 4
sequential states of any of the 16 signals.
Each state for a single signal can be high, low or don’t care. This allows you to trigger on rising edges,
falling edges, edges during another signals constant level, or one edge
followed by another edge.
The waveforms are shown with a trigger position
which represents where the trigger occurred.
This sample point is marked on the waveform display with a Vertical red
dotted line and a “T” in the horizontal cursors bar.
You can use the Trigger Position setting to specify how much of the data that is in
the sample buffer comes before the actual trigger position. If you place the Trigger Position all the way
to the left, most of the samples taken will be after the trigger sample. If you place Trigger Position all the way to
the right, most of the samples taken will be before the Trigger sample. This control lets you see what actually
happened way before or way after the trigger occurred.
 
Trigger
Position to the Right Trigger Position
to the Left
Waveform Display and Zoom Settings
The Waveform display area is where the measured
signal information is shown. It is
displayed with time increasing from left to right and voltage increasing from
bottom to top. The screen is divided
into Divisions to help in measuring
the waveforms.
The position of the waveform defaults to show the
actual trigger position in the center of the screen after a capture. However, you can move the display to see what
happened before or after the trigger position.
To Scroll
the Waveforms in Time left and right, you can use the scroll bar at the bottom
of the waveform display (right above all of the controls), or you can simply
click and drag the waveform itself with the left mouse button.
To Scroll
the Analog Waveform in Voltage up and down, you can use the scroll bar at
the left of the waveform display (one for each channel), or you can simply
click and drag the waveform itself by using the colored bar to the immediate
left of the actual waveform.
To change the number of Seconds per Division use the scrollbar at the bottom left of the
waveforms. To change the number of Volts per Division for an analog
channel, use the scrollbars at the left of the analog waveforms. You can also zoom in and out in time by
clicking on the waveform. To zoom in,
click the left mouse on the waveform window.
To zoom out in time, click the right mouse button on the waveform
window.
The Display section of
the screen shows three selections that affect the way the waveform is
displayed.
The Wide
setting shows the wave using a wider pixel setting. This makes the wave easier to see.
The Vectors
setting draws the waveform as a line between adjacent samples. With this mode turned off, the samples are
shown simply as dots on the display at the sample position.
The Persist
mode does not clear the display and writes one trace on top of the other trace.
The benefits of these display modes can be seen
when you are measuring fast signals and want to get more resolution out of the
oscilloscope than the maximum sample rate allows. See the below traces to see the difference. Each trace is taken of the same signal, but
the right one shows much more wave detail over a short time of display updates.
Persist = OFF, Vectors = ON, Wide = ON
Persist = ON, Vectors = OFF, Wide = ON
Measurements and Cursors
The main reason for
using an oscilloscope or logic analyzer is to measure the various parts of a
waveform. The USBee DX uses cursors to
help in these measurements.
The X1 and
X2 Cursors are placed on any horizontal sample time. This lets you measure the time at a specific
location or the time between the two cursors.
To place the X cursors, move the mouse to the gray box just below the
waveform. When you move the mouse in
this window, you will see a temporary line that indicates where the cursors
will be placed. Place the X1 cursor by
left clicking the mouse at the current location. Place the X2 cursor by right clicking the
mouse at the current location.
The Y1 and
Y2 Cursors are placed on any vertical voltage level. This lets you measure the voltage at a
specific location or the difference in voltage between the two cursors. To place the Y cursors, move the mouse to the
gray box just to the right of the scroll bar to the right of the waveform. When you move the mouse in this window, you
will see a temporary line that indicates where the cursors will be placed. Place the Y1 cursor by left clicking the
mouse at the current location. Place the
Y2 cursor by right clicking the mouse at the current location.
In the Measurement
window, you will see the various measurements made off of these cursors.
·
X1
Position – time at the X1 cursor relative to the trigger position
·
X2
Position – time at the X2 cursor relative to the trigger position
·
X2-X1
– time difference between X1 and X2 cursors
·
1/(X2-X1)
– the frequency or the period between X1 and X2 cursors
·
Y1
Position – voltage at the Y1 cursor
relative to Ground for both CH1 and CH2
·
Y2
Position – voltage at the Y2 cursor
relative to Ground for both CH1 and CH2
·
Y2-Y1
– voltage difference between Y1 and Y2 cursors for both CH1 and CH2
There are also a set of automatic measurements that
are made on the analog waveform for each trace.
These are calculated without the use of the cursors. These are:
·
Max –
the maximum voltage of all samples in the current trace for both CH1 and CH2
·
Min –
the minimum voltage of all samples in the current trace for both CH1 and CH2
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