Bob Lunn
10/21/97 10:08 AM


> Can anyone direct me to where I can get a copy of the
> I2C protocol definition.

     Look at a datasheet for any pic that supports
     SPI/IIC comms, such as the 16C74.  These provide
     quite good descriptions of the protocols.

     Alternatively, look at the datasheets for any
     serial eeprom that uses either of these protocols
     (eg: 24C01 for IIC or 25LC040 for SPI).

     All of these datasheets are available from the
     Microchip web site.

> Is I2C better than SPI??

     As usual, it depends.

     'Standard' IIC only provides data transfer rates
     up to 100kHz, though 'fast' IIC goes to 400kHz.

     In contrast, standard SPI goes to 2MHz.

     The choice is usually based on the hardware that
     you want to use.  If your hardware requires SPI
     then you use that; if it requires IIC ditto.

     In the absence of a hardware constraint I always
     choose IIC.

> What are the differences between the two?

     SPI is owned by Motorola.

     IIC is owned by Philips.

     :)

> Does anyone have any examples of I2C or SPI code using
> a 16F84?

     I believe there are appnotes showing bit-banged IIC
     on the Microchip web site, but I don't know the number.
___Bob