[sdiy] A/D weirdness

[Jay Schwichtenberg]

Karl,

The high-z mode would require a pull up if you were to use it don't forget
that. I would say that it depends on the ADC chip whether or not it is
perferable. If they have sloppy timing then yes I would poll the data bit.
By sloppy timing I mean that sometimes it takes 5 clocks, sometimes 7 clocks
... before the data comes out. If they have good timing then it is ok and if
I remember correctly the data sheet says 4.5 to 5 clocks. So that should be
ok. The reason they keep the chip in high-z is to have multiple devices on
the buss. Only the active one selected by the chip select should switch out
of high-z and go active on the bus.

Good luck and happy holiday!
Jay

-----Original Message-----
From: Karl Ekdahl [mailto:elektrodwarf at yahoo.se] 
Sent: Saturday, December 24, 2011 9:00 AM
To: Jay Schwichtenberg; synth-diy at dropmix.xs4all.nl
Subject: SV: [sdiy] A/D weirdness

Jay

I'm just counting the clocks - i didn't even reflect on the high-z mode
being usable for polling, is this somehow preferable?

Karl



----- Ursprungligt meddelande ----
Från: Jay Schwichtenberg <jays at aracnet.com>
Till: 'Karl Ekdahl' <elektrodwarf at yahoo.se>; synth-diy at dropmix.xs4all.nl
Kopia: 
Skickat: torsdag, 22 december 2011 22:22
Ämne: RE: [sdiy] A/D weirdness

Karl,

Are you counting clocks or polling for Dout to put out the 0 start bit
before you start reading data?

If you are polling for the first Dout 0 you should have a pull up on it.
It's in hi-z mode before data comes out.

Good luck.
Jay S.

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Karl Ekdahl
Sent: Thursday, December 22, 2011 4:32 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] A/D weirdness

>Do you sample your bits a little on the edge of things?

>Could you have something else interupting your data-reading process 
>somehow, so you miss timing.

Good point, i never disabled interrupts before during this operation - sadly
this didn't do the trick. I rewrote the entire data retrieval algorithm,
doing everything exactly as described in the datasheet - it sure screwed
with other pieces of my code, but the data is still erratic.. nnnhgg very
annoying. 

Karl

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