AVR-Chat

Glad I could help.

Jim

>
> 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
>>
>>
>>
>> ------------------------------------
>>
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>>
>>
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