On 1/14/07, Philip Pemberton <piclist@philpem.me.uk> wrote:
> Mark Rages wrote:
> > I had to make the some changes to use AN734 (I2C slave example) on a
> > 16F690.  For more information, including an idea for testing I2C, see
> > my blog. (http://vivara.net/blog/?p=53)
>
> If you want to know why the address is 'halved', it's probably because I2C's
> address field is 7 bits with a 1-bit read/write flag bit in the LSB. SMBus
> takes the address as those seven bits, LSB-aligned, with separate R/W
> operations on the SMBus controller.
>
> The PIC is comparing the address with 0x06 (write to real address 0x03), your
> PC is writing to what it calls address 0x03. So the R/!W bit is low (write),
> meaning the address byte has a value of... 0x06.
>
> I'm not 100% sure if this is what's actually happening, but the theory seems
> to be accurate... YMMV.

I suspected something like that, but I didn't dig through the specs to
verify it.

Oh here it is, in the '690 datasheet, section 13.12.1:

> The value of register SSPSR<7:1> is compared to the value of the SSPADD register.

Regards,
Mark
markrages@gmail
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