[sdiy] nice Digi Pot

Roman Sowa modular at go2.pl
Tue Jun 28 08:53:46 CEST 2016


That is turning into childish battle "my SPI is better than your SPI".
What's the diffrence, who cares? If you want low pin count, chain 64 
devices. If you want fast response, use individual chip selects, or 
distributed decoder to address 64 lines out of 6 pins.
I'm controlling 24 inputs and 24 outputs in one board using only 4 pins 
and I could chain it up to a thousand probably, limited only by tiny 
microcontroller RAM size, but I also have 64-output device where SPI is 
split into 4 groups with 4 chip selects. Everything is the ballance 
between speed of update and routing simplicity.

Roman

W dniu 2016-06-28 o 00:18, Vladimir Pantelic pisze:
> On 27.06.2016 23:48, jays at aracnet.com wrote:
>> Off the top of my head the only thing that I can think of is the
>> amount of time
>> to do the operation.
>
> that is one reason, but having to use only a few pins to control a lot
> of devices is another. if I want to control 64 of these digipots I would
> need 64 chip select pins or some external logic to make some kind of 1
> to 64 demuxer. with daisy chaining I would need only CS/CLK/MOSI and be
> done. add DMA pushing data to SPI and you even have zero CPU overhead....
>
>> I haven't ran across any SPI or I2C devices out there that do daisy
>> chaining and
>> I've used a fair number. A lot of the FPGA chips I've had to deal with
>> do this
>> do and some of the 'smart' LEDs do daisy chaining. Are there any
>> SPI/I2C chips
>> out there that people know about?
>
> the ADG1414 mentioned in the other thread today. I have a design where I
> control 32 of them with just 4 CPU pins...
>
>
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