> -----Original Message-----
> From: Roman Black [SMTP:fastvid@EZY.NET.AU]
> Sent: Friday, May 18, 2001 8:13 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: I2C slave software for the PC to talk to a PIC
>
> > > From: James Newton [SMTP:jamesnewton@PICLIST.COM]
> > > Sent: Thursday, May 17, 2001 4:40 PM
> > > To:   PICLIST@MITVMA.MIT.EDU
> > > Subject:      [PIC]: I2C slave software for the PC to talk to a PIC
> > >
> > > The I2C resources on the piclist.com site and in the archives and on
> > > google
> > > don't seem to include PC I2C slave software...
> > >
> > > ...which would seem to be very useful for testing PIC I2C masters...
> > >
> > > ...am I just missing it?
>
> Michael Rigby-Jones wrote:
> > Reason being it is very difficult to write a pure bit bashed slave on a
> PC
> > that will run at reasonable speeds.  You really need a small amount of
> > external logic to make this feasable, something to detect stop/start
> > conditions, and a shift register.
>
>
> Olin Lathrop wrote:
> > What hardware would you have the PC use for IIC?  "Standard" PCs don't
> come
> > with IIC ports.  IIC requires two open collector drivers.  I vaguely
> > remember that some of the parallel port control lines are open
> collector,
> > but am not sure.  Even if so, you would need to write a custom kernel
> mode
> > device driver to mess with the parallel port in a non-standard way.  It
> > would be easier to hook a PIC to a serial port or parallel port and have
> it
> > do IIC for the PC.
>
>
> Yeah, it can be done fine. I'm always connecting PIC
> stuff to my parallel port. I don't see the speed as
> much of a problem, 100kbps should be fine, don't know
> if you would get 400kbps but it might be possible.
>
> I would use 3 pins of the PC par port, 2 as inputs for
> the SDA and SCL, and one (output) through a diode which
> would be used to pull the SDA low for acks etc. Probably
> 3 resistors and one diode needed.
>
> I write stuff in Turbo C for dos, you can read and write
> the port with ONE asm instruction and provided you can
> go to dos mode and kill that windows POS you can get
> some pretty impressive port performance. That's one
> reason I stick with Win95, you can force dos mode.
>
> The lead length is not that critical at 100kbps, probably
> a few feet would be ok. :o)
> -Roman
>
Roman,

You are talking about an I2C Master implementation which is pretty trivial
compared to a slave.  I'm starting to get interested in designing a cheap
bus analyser though.  Will have to do some "back of envelope engineering" at
lunch time!

Mike

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