AVR-Chat

Thank you Jim,

I finally get it : - S
I had mi mind set on a different meaning and couldn't get out of it...

I suppose the inconsistencies in terminology between manufacturers doesn't help either... one registers and one samples; one "drives data out" and one does "setup"... ah maaaaan

Thanks again,

Cat


> To: AVR-Chat@yahoogroups.com
> From: wagnerj@proaxis.com
> Date: Tue, 1 Sep 2009 10:58:53 -0700
> Subject: Re: [AVR-Chat] I don't understand SPI graph in      "ATmega164P/324P/644P" Datasheet (NEW)      8011M�AVR�08/09
> 
> >
> > Hi there,
> >
> > Looking at Fig. 15.3 (Pg. 167) and reading the "15.4 Data Modes" paragraph
> > on Pg. 166, I don't see that:
> >
> >    "Data bits are shifted out and latched in on opposite edges of the SCK
> > signal"
> >
> > I thought that means that Data Out is valid on MOSI on Rising SCK and Data
> > In is Sampled on MISO on Falling SCK (or the other way)
> > but it looks like nothing happens on Falling SCK...
> >
> > I need to know which mode to choose because on the AD9874:
> > "All data input to the AD9854 is registered on the rising edge of SCLK,
> > and all data is driven out of the AD9854 on the falling edge of SCLK."
> >
> > What don't I get, please?
> >
> > Thanks,
> >
> > Cat
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> 
> Hi Cat -
> 
> It may just be a mixup of words or maybe a misunderstanding of the SPI
> process.
> 
> On the shifting edge of the clock, data is changing and is NOT valid. It
> IS valid about half way through a clock cycle where the opposite edge
> occurs. Maybe this is what you were trying to write and it just didn't
> quite come out that way.
> 
> Give the specs of the AD part, you want to shift the data out from the
> micro on the falling edge of SCLK. It will be latched by the AD part on
> the rising edge, as described. Since SPI interface is just a fancy shift
> register, the input and output shift on the same edge.
> 
> Jim Wagner
> Oregon Research Electronics
> 
> 
> 
> ------------------------------------
> 
> Yahoo! Groups Links
> 
> 
> 


[Non-text portions of this message have been removed]