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Compared to an Oscilloscope, What Information Does a Protocol Analyzer Provide about Waveforms?
Rena Ayeras

Question from the Customer:

I am troubleshooting the serial bus of a system with an oscilloscope. In addition to the electrical characteristics, I need more details to understand the performance of the system. I am looking at the Beagle I2C/SPI Protocol Analyzer – what details can it provide me about waveforms?

Response from Technical Support:

Protocol analyzers and oscilloscopes are essential debugging tools. They differ significantly in usage and application, such as the low-level and high-level attributes of signals. We will begin with an overview of the technical benefits of each tool, and then go into the details of what a protocol analyzer provides.


Oscilloscopes are useful for debugging systems, especially for electrical issues just as jitter, noise, signal to noise ratios, and other signal distortions. This visual diagnostic can be a quick diagnostic, shedding light on some of the most crucial parameters of low-level signal conditions.

Unlike oscilloscopes, protocol analyzers, like the Beagle I2C/SPI Protocol Analyzer, allow designers and developers to debug their embedded systems at a much higher level of signal data. For analyzing data traffic, protocol analyzers provide significant information.

Protocol Analyzers

There are two forms of protocol analyzers: software and hardware.

  • A software analyzer offers an economic advantage. Its limitation is within the capabilities of the host computer’s hardware.
  • A hardware analyzer can debug embedded hosts, providing visibility to issues related to timing, transmission, and speed negotiation.
Beagle protocol analyzer with product box

Analyzing Data Packets

An advantage of using protocol analyzers is allowing developers to view data in the form of packets, not just individual bit streams. Protocol analyzers also offer a real-time display of captured data, which can speed up the process of debugging a system.

Some ability of frequency measurement is available through the Timing Details window of the Data Center Software, an application that displays the data captured by a Beagle protocol analyzer. The Details window (Detail->Timing) provides lower-level detailed information about a transaction, which is described in the following sections.

Bit-Level Timing

The Timing pane of the Details window provides bit-level timing for the data of I2C and SPI transactions. Each byte of the transaction appears as a row in the Timing pane. All the bytes from the transaction are displayed in this pane, including start and stop conditions. The first line of the table displays the transaction timestamp as well as the transaction duration, both to nanosecond precision.

Viewing waveforms via Data Center Software Data Center Software Timing Pane

Each row contains the following information:

  • Offset: The offset position of the byte.
  • Time: The time in nanoseconds from the start of the transaction to the start of the byte.
  • Value: The hexadecimal value of the byte.
  • Timing: A graphical display of each individual bit of a byte. Each bit is displayed as either high or low with the time in nanoseconds from the start of the current bit to the start of the subsequent bit.

Please note - the lengths of the timing blocks in the graph are not drawn to scale. They show the relative timing of one bit to the next. Depending on the protocol, the bit order may be MSB or LSB. The column label shows the bit order: MSB (b7...b0) or LSB (b0...b7).

  • For the I2C protocol, the timing mode displays 9 bits per line. The ninth bit is the ACK/NACK bit.
  • For the SPI protocol, the timing mode displays both MOSI and MISO signals.

For more information about the advantages of protocol analyzers, see this article Protocol Analyzer: Must-Know Advantages for Embedded Systems.

Here is an example of using an Aardvark I2C/SPI Host Adapter with the Beagle I2C/SPI Protocol Analyzer for prototyping.

We hope this answers your question. Additional resources that you may find helpful include the following:

If you want more information, feel free to contact us with your questions, or request a demo that applies to your application.