> -----Original Message-----
> From: Donovan Parks [SMTP:dparks@UVIC.CA]
> Sent: Thursday, April 26, 2001 11:49 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [PIC]: Having 16f877 talk to each other.
>
> Hello,
>
> I need a bunch (max 6) 16f877 pic's to be able to talk to each other.
> From
> the literature on the Microchip site I gather I can use SSP with
> SPI(Master
> Mode) and I2C(Master/Slave).  Is this the only(best) way to have my pic's
> talk?  What are the benefits of SPI to I2C?
>
> Thanks for all help.
>
> Donovan
>
The advantages of SPI are: higher bit rate (Megabits/s possible on some
devices), more simple and robust protocol (i.e. no start or stop
conditions).  It is also more simple to bit bash SPI in software than I2C.

The downsides of SPI are: Chip Select wire needed for every slave device.
If you have several slaves, you'll be using up pins on your PIC pretty
quickly.

It sounds like you are going to require a Multimaster bus, which is possible
with I2C and Microchip even have an app note on this.
I don't know about SPI and multi-master systems, it should be possible with
some kind of arbitration.  However, if your network 'o' PIC's really need to
talk to each other, i.e. any PIC and send and recieve to/from any other PIC,
then SPI is going to be hard work to implement.  I'd suggest sticking to
I2C.

Regards

Mike

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