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I2C vs SPI

 
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cfernandez



Joined: 18 Oct 2003
Posts: 145

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I2C vs SPI
PostPosted: Tue Jan 11, 2005 12:05 pm     Reply with quote
Which is the difference between I2C and SPI and which the best option?

I use a I2C eeprom in my project, but now I am evaluating use SPI eeprom (www.ramtrom.com). The only difference is that the SPI (25Mhz) is more fast that I2C (1Mhz), but really the CCS take this advantage?

If somebody can tell me your opinion? Thank you very much!!

Best Regards,
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Tue Jan 11, 2005 1:12 pm     Reply with quote
Quote:
The only difference is that the SPI (25Mhz) is more fast that I2C (1Mhz), but really the CCS take this advantage?
In the PIC processor the fastest SPI rate you can get is using the internal SPI hardware. The maximum SPI frequency is then CPU-clock / 4. Assuming you are running at the maximum speed of 40MHz for a PIC18, then your SPI-clock will be 10MHz. So your SPI eeprom is much faster than the maximum SPI-clock achievable in the PIC.

I2C advantages:
- Good software I2C simulation by the the CCS compiler (if you want to use the hardware I2C for something else).
- Requires only 2 I/O pins (SPI requires 3 + 1 select line for every device).
- Multiple masters possible on the same bus.

SPI advantages:
- Faster (higher bitrates and no overhead for addressing etc.)
- Easier protocol (no multi-master, etc).
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