Why isn't 4B5B used like I2C, SPI? [closed]

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I was explaining I2C/SPI serial protocols to my friend when he mentioned there's a way to send data between two devices using one wire with the 4B5B protocol. If this is true, why isn't 4B5B used to, say, send data between arduino and peripheral devices?

Answer 1

The short answer is that 4B5B isn't a protocol you can use while I2C and SPI are.

I2C and SPI qualify as OSI Network level 1 and 2 specifications, covering both physical electrical specifications of connection between devices and how the connected devices use the connection to communicate. 4B5B is merely a bit encoding scheme, covering only how to represent 4 bits of data in 5 bits of signal to ensure that the resulting signal has adequate auto-clocking content. 4B5B is not a "protocol" or a level 1 or level 2 network specification, meaning that if you try to connect two devices "using 4B5B" you will still have far too many unspecified details to be able to actually create a connection over which you can exchange data.

Answer 2

Here's a not so useful answer: I think the main reason why it is not part of the Arduino platform is that it isn't implemented on most of the chips on which Arduino is built:

• Arduino Nano and Uno are based on ATmega168/ATmega328. Neither 168 nor 328 have 4B5B nor Dallas 1-wire protocol support.
• Arduino Due uses ATSAM3x8e. It likewise lacks support for one-wire protocols
• Arduino Lenonardo uses a different AVR-architecture chip, the ATmega32u4, but same story.

In the end, the question probably should be put to Atmel rather than Arduino designers.