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iOS logic analyzer shows the bits

-May 25, 2012

LogiScope logic analyzer for iPad and iPhone, Oscium, www.oscium.com. Price $389.

Oscium, the company that developed the iMSO-104 oscilloscope and WiPry WiFi spectrum analyzer/power meter, have now developed a 16-channel logic analyzer for the iPad, iPhone and iPod Touch. I tried the LogiScope on an iPad 2 rather than on an iPhone because of the iPad's larger screen. Viewing 16 traces on the iPhone's screen is, well, challenging.

As Figure 1 shows, the LogiScope comes with two wiring harnesses, each holding eight color-coded input wires

 Oscium_Logiscope_Fig1
Oscium's LogiScope comes with two 8-channel harnesses and 16 test clips. Click on image to enlarge

and a ground wire. Yes, the black wire is ground. The leads connect to standard-size pins. It also comes with a bag of 16 clip leads. I used 16 channels of a 24-channel logic demo board as a signal source.

After downloading the free app from the App Store, I connected the LogiScope's 16 inputs. The iPad immediately found the instrument and signals appeared. Navigating the menus is easy and similar to Oscium's other products. Each trace on the screen is color coded to match the color of the wire. Using your finger, you can move any trace up or down the display.

The "Digital" menu lets you turn on any channel and give each a name. Figure 2 shows bit 07 renamed "clock." The "Cursor" menu lets you enable cursors for measuring time between events or the frequency of a signal. Using the "Measure" menu, you can measure duty cycle, pulse width, and frequency on any channel. You also get a two-level trigger. Virtual logic gates add combinational logic for building a trigger. The gates let you set up AND, NAND, OR, NOR, XOR, or XNOR conditions to trigger an acquisition. Trigger conditions include rising or falling edges, levels, or pulse width.

Digging deeper into the menus revealed that the LogiScope can trigger not just on two channel levels or edges, but

 Oscium_Logiscope_Fig2
Figure 2. You can change the name of any signal. Here, D07 is renamed "clock." Click on image to enlarge

on digital words that are greater then, less than, or equal to preset values. In fact, the LogiScope can trigger on pattern values expressed in decimal, binary, octal, hexadecimal, or even ASCII format. Thus, the instrument can trigger on, say xx1A hex (channels 0-7) and only when channel 14 contains a rising edge. Figure 3 shows how to set that value. Once you have a value set, you can move the trigger bits around with your finger to change the trigger-pattern's value. That lets you take advantage of the touch capabilities of the iOS.

The iOS touch capabilities also let you zoom in on a portion of the waveform simply by spreading two fingers horizontally. Spreading your fingers vertically also lets you zoom in on a condition of interest. Figure 4 shows that I zoomed in on the glitch in bit 14. Timing ranges from 10 s/div to 1 µs/div. There are ten divisions across the screen that the screen can display as lines or dots. Sliding your finger across the screen lets you scroll across the captured waveforms. You can use the settings menu to capture screen images and e-mail them without leaving the LogiScope environment. That's a time saver and a nice convenience. In fact, you can e-mail a screen image without even capturing it.

The LogiScope also lets you decode serial-bus data streams for UART, SPI, and I2C, and parallel buses through the "Decode" menu. It works with Works with 2.0 V, 2.5 V, 3.3 V and 5.0 V logic levels and speeds up to 100 MHz.

 Oscium_Logiscope_Fig3
Figure 3. Triggers can be set based on bus values. Click on image to enlarge


The LogiScope is a powerful tool for debugging and troubleshooting digital systems on the road or at the bench. Its $389 price tag is a "bit" high especially if you need to buy an iPad as well. Fortunately, you don't need the higher-resolution screen on the New iPad for this app. For the next software revision, I'd like Oscium to have the host device automatically send an e-mail or other alert to your phone when the LogiScope triggers. That would let you walk away from the screen until the wanted condition occurs. 

 

 

 Oscium_Logiscope_Fig4
Figure 4. Use your fingers to zoom in on a waveform. Click on image to enlarge

 

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