I2C vs SPI Protocol Analyzers: Differences and Similarities

What do you choose for I2C and SPI protocol analyzers? Let's take a look at their differences and similarities.

About the I2C

I2C (Inter-Integrated Circuit) is an on-board communication protocol, which is ideal for short distances and low bandwidth. It has a master-slave architecture in which all slaves are connected to the master via two wires: the serial data wire (SDA) and the serial clock wire (SCL). I2C is typically used for attaching lower-speed peripherals such as sensors to processors and microcontrollers over short distances within an integrated circuit.

The I2C protocol defines how to send data.  Initially, the master issues a start condition followed by the address of the slave device to which it is communicating.  Once the appropriate slave has identified its address, it looks for the proceeding read/write flag issued by the master. This flag tells the slave whether it can expect to receive data or send data. Once the slave has acknowledged the master, communication then proceeds.

One feature of I2C is the built-in check system: every byte of data is acknowledged by the receiver with either an ACK or NAK to signal to the transmitter the data has or has not been received. Once the master has finished communicating with the addressed slave, it will issue a stop condition to signal the end of transmission.  After the stop condition, communication with other slave devices can begin.

About the SPI

The Serial Peripheral Interface (SPI) is another serial communication protocol that is heavily  used in embedded systems. Like I2C, it is also has a master-slave architecture but it is a 4+ wire bus.  SPI requires a clock line (SCK), two data lines for transmitting data bidirectionally known as the MOSI and MISO lines.  Additionally, there must be a slave select (SS) line for each slave on the bus.  Instead of utilizing an addressing system like I2C, multiple slaves are controlled by the master via the slave select lines. This is a very simple protocol with almost no overhead, making it ideal for streaming applications - data can be shifted at very high rates as the full duplex characteristic makes SPI a very efficient protocol.

If you need to monitor the data communication of these protocols you will require a protocol analyzer. Protocol analyzers capture and report the communication across a bus for the purpose of allowing users to analyzer and debug data traffic.  Let’s have a look at similarities and differences between properties of I2C and SPI protocol analyzers.

I2C vs SPI Protocol Analyzers: Differences and Similarities

One significant difference is the I2C is mucher slower (typically 100-400KHz, maximum 5 MHz) as compared to SPI, which can go up to 80MHz or sometimes even higher speed. The availability of higher SPI speed is due to the use of multiple lines for data transmission and little protocol overhead.

Now that we have a clear understanding of the differences and similarities between the two protocols, let’s discuss the analyzers.

There are several protocol analyzers on the market. Some are specific to one protocol while other analyzers support multiple protocols.

There are few functional differences between most of the I2C and SPI analyzers. They might have implementation differences such as header types, pin counts, or voltage/current tolerances, but those differences are from the manufacturers' designs.

Most analyzers provide a  GUI software to read the communication captured on the bus. Protocol analyzers typically decipher protocol control signals and data, as opposed to a standard logic analyzer that only displays signals and timing diagrams.

Not all software is created equal. The ability to view data in real time, start and stop captures, save and share captures and search and filter captures are not always available in all protocol analyzer software. For additional flexibility and use, some protocol analyzers come with a software API allowing the user to created a customized tool for their specific needs.

There are a few protocol analyzers on the market that support multiple protocols, but again - not all are created equally. These analyzers can range widely in price and functionality. The Beagle I2C/SPI Protocol Analyzer monitors I2C and SPI protocols, as well as MDIO. It is compact, relatively inexpensive and the accompanying software offers real-time data capture and display and fully supports Window, Linux, and Mac OS X.

Beagle I2C/SPI Protocol Analyzer Promira Serial Platform

Figure 1: Beagle I2C/SPI Protocol Analyzer

Figure 2: Pormira Serial Platform

If you are looking for increased performance, additional protocol support and a build-it-as-you-need-it device, consider the Promira Serial Platform. The Promira platform is an I2C, SPI host adapter as well as an eSPI protocol analyzer, all in one.  Protocol analyzer functionality for I2C and SPI will be added to the platform in the near future.  The platform model allows customers to purchase only the applications they need, as they need them.  It comes with a slightly higher ticket price than the Beagle I2C/SPI Protocol Analyzer - it also comes with a lot more options.

Understanding the similarities and differences between protocol analyzers is important and can be the difference between delivering early and missing a deadline.

When shopping for a protocol analyzer, consider its OS compatibility, USB options as well as the price. Make sure you do your research, get exactly what you need and know the limitation of what you purchase.  Considering all the available options will not only help you save your money, it will also maximize your work performance - you, your team and your projects get the most out of it!

If you have any questions about our protocol analyzers or other Total Phase products, feel free to email us at sales@totalphase.com. If you already own one of our devices and have a technical question, please submit a request for technical support.

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