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10 bit I2C addressing

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vikky.saraswat

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Hi all,

I was going through the specs of the I2C and found that 10 bit addressing mode is been supported. My question is with the basic 7 bit address we can address 128 different devices, but due to capacitance effect we can't able to connect all the 128 devices at one time to any system.

So why the 10 bit addressing was been introduced since with the basic 7 bit addressing bits itself, we are unbale to connect all the devices (128) in a single system?? Increasing the addressing bits allows us to address more devices (2^10). How 10bit addressing have an upper hand on the 7bit addressing???

Regards
Vikas
 
Just read the specs of a 24lc256 eeprom... This uses three external addresses 0 to 7 as you mentioned but you can have 2 of them at that address.. Other devices are also addressed with software at different, internal addresses... It goes on an on..

The case of how many... your right. If you have say 128 on the bus, you would need to lower the bus pullup resistors to counter act that.
 
Even though we take outmost care, we are limited to number of devices connected to I2C to much less than 128. Or you can say the devices connected to any system through I2C are very limited.

Then why the 10 bit addressing has been formed? Is that the manufactures got more devices and the 7 bit address is not fitting them?

Regards
Vikas
 
The key is in the first paragraph here: https://en.wikipedia.org/wiki/I²C

Slave addresses are allocated by NXP which effectively means there is probably a one to one address space to part number correspondence. So, a 10 bit space means more devices to chose from, NOT more devices in the system. There are ways to significantly increase the number of devices in the system. Look at the bus expander parts.
 
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