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Table of contents
I2C vs SPI
I2C and SPI: Which one should be used
When to choose I2C
When to choose SPI
Is I2C slower than SPI?
Why is SPI faster than I2C.
Is I2C synchronous or asynchronous?
What is SPI communication protocol?
Last Updated: Mar 27, 2024

I2C vs SPI

Author Harsh
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In a communications system, a communication protocol is a mechanism that allows two or more entities to communicate with each other. The rules of communication, syntax, and how the device recovers from failures are all described in communication protocols. Two protocols are widely used to communicate between chips on a printed circuit board: Serial Peripheral Interface (SPI) and Inter-Integrated Circuit (IIC) (IIC or I2C). SPI and I2C are widely popular because they are simple to implement, needing few components and little code. Both use serial communication to convey data and can accommodate several devices on a single bus. SPI and I2C are used to communicate between many microcontrollers, sensors, and peripherals (such as LCDs).

In this blog, we will learn about SPI and I2C protocols, the differences between them, and which one should be used.


The I2C protocol is a serial communication protocol. It supports slow devices well, such as EEPROM, ADC, and RTC, and many others. I2c is utilised not just with single boards, but also with additional external components that are connected to the boards via cables.

It communicates using only two wires. One cable is used for data (SDA), while the other is utilised for the clock (SCL). Both buses in I2C are bidirectional, meaning the master can send and receive data from the slave. The clock bus is controlled by the master, although the slave can suppress the clock signal in particular circumstances.

I2C (Source: ArticleWorld)

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SPI is a four-wire communication protocol that allows microcontrollers to communicate with a wide range of serial bus devices, including temperature and pressure sensors, A/D and D/A converters, memory devices, LCDs, and more. The four-wire layout is a very reasonable way to make data transfer on the serial bus easier. 


SPI (Source: ArticleWorld)

Each of the four wires is associated with a different logic signal:

  • SCLK (Serial Clock): The Serial Clock wire carries the clock signal from the master device to the other serial bus devices.
  • MOSI (Master Output, Slave Input): The MOSI wire transports data from the master device to the slave devices on the serial bus.
  • MISO (Master Input, Slave Output): The MISO wire connects the slave device's data output to the master device or microcontroller over the serial bus.
  • SS (Slave Select): There must be one master device on an SPI bus, although there can be several slave devices. The master device can communicate with all slave devices, however slave devices can only communicate with the master and not with one another. Before delivering a data transmission, the master device utilises the Slave Select wire to select which slave device on the bus it will communicate with.

    You can also read 8051 Microcontroller Pin Diagram here.

I2C vs SPI

Also see, Difference Between Verilog and Vhdl

I2C and SPI: Which one should be used

Both I2C and SPI have their own advantages and disadvantages. Choosing one out of two really depends upon the requirement of the project. Below are some valid points which can help you to choose the best protocol for your project.

Speed comparison: I2C data transfer speeds were originally set at 100kbps, however they have been increased to 400kbps and even 5Mbps in Ultra Fast mode. SPI, on the other hand, does not specify a maximum—or any—communications speed and can be used at speeds of up to 10 Mbps.

Unless you have a compelling need to use I2C, it's frequently best to use the SPI protocol if you can afford the extra expense.

When to choose I2C

  • When the project demands transmission distances greater than 10 metres, with severe noise and interference.
  • When the project demands the use of several master devices, which is not supported by the SPI standard.
  • On-chip space is limited, thus having only two wires rather than four, then I2C interface is preferable.

When to choose SPI

  • SPI is a better option if you need to deliver data at a faster rate.
  • For a small number of peripherals that need to transfer a high volume of data, SPI is a superior option.
  • SPI draws less power as compared to I2C, So it is better to use SPI when low power consumption is required.


Is I2C slower than SPI?

Yes, I2C is slower than SPI. I2C data transfer speeds were originally set at 100kbps, however they have been increased to 400kbps and even 5Mbps in Ultra Fast mode. SPI, on the other hand, does not specify a maximum.

Why is SPI faster than I2C.

In contrast to I2C, which employs "open-drain drive mode with a resistive pull-up," SPI uses "strong drive mode" to drive the bus. Strong drive mode pins can charge/discharge the bus to the rated voltage levels considerably faster than weak drive mode pins.

Is I2C synchronous or asynchronous?

I2C is a synchronous protocol, which means that the communicating parties do not have to agree on a speed in advance.

What is SPI communication protocol?

The Serial Peripheral Interface (SPI) is a synchronous serial communication interface specification used largely in embedded systems for short-distance communication. Motorola created the interface in the mid-1980s, and it has since become the de facto standard.


In this article, we have extensively discussed SPI and I2C protocol, their differences, and which one should be used.

We hope that this blog has helped you enhance your knowledge of I2C and SPI Protocol and if you would like to learn more, check out our articles on our Website

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