Our support for MathWorks MATLAB now includes a driver for the PicoScope 2000 Series "A API" devices using the ps2000a driver. This supports the PicoScope 2206A, 2207A and 2208A oscilloscopes and the PicoScope 2205 MSO. An updated version of the driver, packaged with example code, is now available on the MATLAB Central File Exchange.
[Amendment 24 March 2016: This driver was previously included in the ps2000a SDK available from picotech.com. The package recently uploaded to MATLAB Central File Exchange includes updated examples and corresponding published HTML files.]
When you're sampling a repetitive waveform with PicoScope, you probably use the Repeat or Auto trigger modes. After each capture, the software on your PC resets the scope hardware to wait for the next trigger event. During this setup process, the scope is not available to capture a new waveform, resulting in a "dead time" of a millisecond or more between captures. Events that occur during the dead time, such as digital bus activity, could be missed.
To shorten this dead time, most PicoScope oscilloscopes offer a Rapid trigger mode. This uses hardware in the scope to capture multiple waveforms without waiting for the software, and can reduce the dead time to one or two microseconds. (For details, see the PicoScope data sheet for your scope model.) Rapid trigger mode is available only on fast timebases and is limited to the number of waveforms that will fit in the scope's buffer memory. With deep-memory scopes such as the PicoScope 3000 Series with up to 512 MS of buffer memory, or even the PicoScope 6000 Series with buffer sizes up to 2 GS, this is unlikely to be a significant limitation.
To use Rapid trigger mode:
At last month's Embedded World show, the Pico Technology stand was popular with journalists as well as the general public. Fortunately Trevor Smith, our Business Development Manager, was on hand to answer questions. You can see two interviews with Trevor on YouTube:
Q. I'm having trouble decoding USB 1.1 12 Mbps signals using PicoScope. What could be wrong?
A. The key thing to remember is that USB uses two signal lines, D+ (green) and D− (white), so you need to use two probes. Connect channel A to D+ with the probe ground lead to ground (black). Connect channel B to D− with probe ground lead also to black. Both probes should be switched to the X10 setting and x10 selected under the Channel Options in the software for each channel.
In order to pick up communication, the host computer and peripheral device have to be actively communicating with each other. For example, if you want to monitor a USB pen drive, you will need to do it while it is transferring a file.
Set the voltage range to ±5 V and the timebase to a suitable time range. The signal should be around 3.3 V and channel B will be the inverse of channel A. If you do not see 3.3 V on the data lines, you may need to probe at a different point.
Set the Trigger mode to Auto and then set up the serial decoder with DataPlus: A and DataMinus: B. The thresholds will be automatically set up if the voltage levels of the D+ and D− are being displayed correctly. You can change to a shorter collection time such as 100 μs/div to see the packets more clearly.
Q. Tell me more about duty cycle measurements with PicoScope
A. PicoScope 6 can measure the duty cycle of a signal (the time it spends in the high state as a fraction of the cycle time). There are two ways to display this information on the PicoScope screen: as an automatic measurement, or as a graph.
To display as an automatic measurement, click the Measurements button on the trigger toolbar and add a Duty Cycle measurement to the desired channel. The result will show up in a measurements table below the waveform area.
To display as a graph, go to Tools > Math Channels, create a new channel, and in the equation editor click duty and then the desired channel button, such as A. Enable the math channel and a graph of the duty cycle of the selected channel will appear on the scope view.
This process is illustrated in the PicoScope Beta 6.9.5: Duty cycle graphing forum topic.
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