I2C vs SPI: Difference Between I2C and SPI


When it comes to interconnecting devices in embedded systems and digital communication, two popular protocols stand out: I2C (Inter-Integrated Circuit) and SPI (Serial Peripheral Interface). Both protocols serve the purpose of facilitating data exchange between components like microcontrollers, sensors, and peripherals, but they have distinct characteristics that make them suitable for different scenarios. In this, we’ll delve into the details of I2C and SPI, highlighting their differences and use cases to help you choose the right protocol for your application.

Basics of I2C and SPI:

What is I2C Protocol?

I2C stands for Inter-Integrated Circuit. I2C is a simple two-wire, half-duplex, serial protocol used to communicate between two devices or chips in an embedded system. I2C has two lines SCL and SDA, SCL is used for clock and SDA is used for data. This synchronous, multi-master, multi-slave serial communication protocol was initially developed by Philips (now NXP) in the 1980s.

What is SPI Protocol?

SPI stands for Serial Peripheral interface. SPI is a Four-wire serial communication protocol. SPI follows master-slave architecture. SPI is a Full duplex synchronous serial communication protocol that uses multiple lines for data exchange – usually four lines: MOSI (Master Out Slave In), MISO (Master In Slave Out), SCK (Serial Clock), and SS/CS (Slave Select/Chip Select). It typically follows a master-slave configuration.

What is the difference between I2C vs SPI?

● I2C is half duplex communication and SPI is full duplex communication.
● I2C supports multi master and multi slave and SPI supports single master.
● I2C is a two wire protocol and SPI is a four wire protocol.
● I2C supports clock stretching and SPI does not have clock stretching.
● I2C is slower than SPI.
● I2C has extra overhead i.e. start and stop bits. SPI does not have any start and stop bits.
● I2C has an acknowledgment bit after every byte of transfer.
● I2C has a pullup resistor requirement.

I2C vs SPI: Key Factors to Consider

Communication Speed:

I2C: Generally, operates at lower speeds compared to SPI due to its multi-device nature and built-in clock stretching mechanism. Speeds are typically measured in KiloHertz (KHz) or MegaHertz (MHz). The frequency range of I2C is 1KHz to 4MHz.

SPI: Offers higher data rates as it doesn’t have clock stretching and supports full-duplex communication. Speeds can range from a few KHz to several tens of MHz The Frequency of SPI ranges from 100kHz to 50MHz

Wiring and Pins:

I2C: Requires fewer pins (2: SDA and SCL) for communication, making it suitable for devices with limited pins or for connecting multiple devices on the same bus.

SPI: Requires more pins for communication (4 or more), which can limit its use in systems with  limited number of pins or when connecting numerous devices.

Topology and Addressing:

I2C: Supports multiple devices on the same bus, each with a unique 7-bit or 10-bit address. Suitable for applications where multiple system components need to communicate with a single controller.

SPI: Typically used in point-to-point or daisy-chained configurations, often with one master and multiple slaves. Slaves can be selected using separate chip select lines.

Noise Immunity and Interference:

I2C: Prone to noise and requires pull-up resistors to function reliably. The clock stretching mechanism aids in handling varying device speeds.

SPI: Generally, more immune to noise due to separate lines for data and clock. However, longer traces might require additional considerations.

Complexity and Overhead:

I2C: Provides built-in flow control mechanisms and supports device discovery (e.g., through the START and STOP conditions). This can introduce overhead in the communication process.

SPI: Offers a simpler communication process but lacks some of the features of I2C like ACK/NACK..

Advantage – I2C:

Easy device add on : It is easy to add new slave devices into the bus. One can add the new device without any addition of slave Select pin as in SPI

Advantage – SPI :

Speed : SPI can support up to 50 Mbps however I2C in the ultra-fast mode can support only 5 Mbps.

Use Cases – I2C vs SPI:

I2C: Ideal for connecting multiple devices to a single controller, such as Sensor arrays, EEPROMs, and Real-Time Clocks (RTC).

SPI: Well-suited for high-speed data transfer applications, like Displays, Flash memory, and Digital-to-Analog Converters (DACs).


In the I2C vs. SPI, the right choice depends on your specific project requirements. If you need to connect multiple devices using fewer pins and can tolerate a bit more complexity, I2C Protocol might be the right fit. On the other hand, if you require higher data transfer speed and a much simpler communication scheme, SPI Protocol could be your go-to option. Understanding the features of each protocol will empower you to make an informed decision that aligns with your application’s needs.

What are the Protocol Analyzers to Debug I2C Protocol and SPI Protocol?

Prodigy offers Protocol Analyzers to monitor, capture and decode the SPI and I2C Bus. Prodigy’s I2C/SPI Protocol Analyzer and Exerciser has the  advanced feature and  capability to not only trigger on a bunch of conditions, but also to capture and store  the data for a long duration of time which is very useful for the embedded design engineers during the debug.

I2C vs SPI

I2C/SPI Protocol Analyzer & Exerciser

Have an I2c related query?  Post here – Prodigy Forum