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'[PIC]: EEPROM (I2C or SPI)?'
2003\04\03@132749 by Konstantin Klitenik

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Can someone point out major advantages and disadvantages of both I2C and SPI
EEPROMs.  I know that SPI is faster and seems to have a simpler protocol.
However I2C uses one less wire.  Microchip only has SPI EEPROM up to 64k but
I2C up to 512k.  Is there anything else I should know about these two and
which one do you prefer?


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2003\04\03@133619 by Jai Dhar

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I can answer the preference part with no problems. I first learnt of SPI while
working with a digital pot with an SPI interface. I wasn't even aware my '628
had an SSP, so I thought the only way was to bit-bang the SPI interface, which
I did. It worked on first try!!! It was so easy, so I was content with it. When
trying to interface an I2C Temp sensor however, I STILL have not been able to
get it work. This is both using the MSSP of an '877 and bit-banging.

Of course, the reason why I can't get it working isn't I2C's fault, it's my
own error - but naturally, one tends to prefer the easier route (whether it be
right or wrong). So that's my opinion....

Jai

Quoting Konstantin Klitenik <spam_OUTkostyan5TakeThisOuTspamHOTMAIL.COM>:

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2003\04\03@160926 by Olin Lathrop

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> Can someone point out major advantages and disadvantages of both I2C
> and SPI EEPROMs.  I know that SPI is faster and seems to have a simpler
> protocol. However I2C uses one less wire.  Microchip only has SPI
> EEPROM up to 64k but I2C up to 512k.  Is there anything else I should
> know about these two and which one do you prefer?

That sums up most of it.  I recommend IIC unless it's not fast enough.


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2003\04\03@161637 by Brendan Moran

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>Can someone point out major advantages and disadvantages of both I2C and SPI
>EEPROMs.  I know that SPI is faster and seems to have a simpler protocol.
>However I2C uses one less wire.  Microchip only has SPI EEPROM up to 64k but
>I2C up to 512k.  Is there anything else I should know about these two and
>which one do you prefer?

I prefer I2C.  Simply because it is a bus, and not a point-point
protocol.  The more SPI devices you use, the more pins you have to use on
your micro for enable lines.  I2C allows a lot of different devices to be
hung off of the same 2 pins with addressing to separate them.  It is a more
complex protocol, but that is not a weakness, it is an advantage.

Furthermore, I2C is a multi-master bus.  This means that if you want 2 MCUs
to have access to the same EEPROM, it's not a problem.  If you then want
those two MCUs to talk to each other, it means no change in hardware.

SPI speed is limited by the speeds that both ends are rated for.  I2C can
handle 3 speed groups IIRC.

The base I2C spec is 100kbps and 7-bit addressing.

I2C now has 2 alternate speed modes, and an additional addressing mode.

Fast mode allows 400kbps
High Speed mode allows 3.4Mbps

10 bit addressing allows an additional 1024 device addresses

Hope this helps,

--Brendan

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2003\04\03@162210 by Stef

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Olin Lathrop wrote:

>>Can someone point out major advantages and disadvantages of both I2C
>>and SPI EEPROMs.  I know that SPI is faster and seems to have a simpler
>>protocol. However I2C uses one less wire.  Microchip only has SPI
>>EEPROM up to 64k but I2C up to 512k.  Is there anything else I should
>>know about these two and which one do you prefer?
>>
>>
>
>That sums up most of it.  I recommend IIC unless it's not fast enough.
>
In that case you can always use FRAM, no write delay ;-)
Stef

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2003\04\04@083308 by Olin Lathrop

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Des Bromilow wrote:
> do you have any reliable or proven asm for the iic?

Yes, but each case is a little different, especially relating to error
recovery.  I don't have any standard IIC routine that has been removed
from and cleaned up from a customer project.


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