I have some suggestion, before you call that there is problem in dsp chip.
Check the following points
1. ADC clock is not more than 5MHz.If it is more, you can get some wrong data
2. if you are using SDK, you don't get the correct 12bit value, the 12bit value
is scaled to 16bit value by SDK.
3. Check ADC reference supply, it must be free from any kind of switching noise
4. if it is your own target board, check the ADC input pin interface respects
the design guide lines given by Motorola.
On Tue, 06 Jul 2004 Bende Georg wrote :
>Yes, I have the same effect. The voltage is about
0,15V and I get values around 32000 in the ADC register. Seems this isn't the
bevhaviour mentioned in the errata.
>Did anyone find a workaround for this issue?
>What annoys me that it seeps to happen only to some of the units.
>Dr. Fritz Faulhaber GmbH & Co KG
>Tel: +49 7031 638294
> -----Ursprgliche Nachricht-----
> Von: Douglas Holub [mailto:d...@comcast.net]
> Gesendet: Dienstag, 6. Juli 2004 16:38
> An: Bende Georg
> Betreff: Re: [motoroladsp] 56F807 DSP failures
> Herr Georg,
> It is a mystery to me. Errata item 4.6 says that
measurements < 24 mV may return a value of 0. Errata 5.6 reccomends
which clocks to use for better accuracy. I had an A/D input on my board
which was > Vdd. It caused some of the A/D measurements to return 32760
all of the time.
> Douglas Holub
> ----- Original Message -----
> From: Bende Georg
> To: m...@yahoogroups.com
> Sent: Tuesday, July 06, 2004 5:05
> Subject: [motoroladsp] 56F807 DSP
> Hello all,
> Recently we have started some test
production, and on about 1% of the units claimed to be defective by our test
software. I took a closer look on these units and I have noticed a huge offset
on 1 or 2 of the ADC channels. At 0V level it showed the same value as the other
-good- ones at 1V, while the whole measuring range is calibrated to 3V. Did
anyone meet such a symptom before? Is it a typical DSP fault or some kind of
design flaw? I have checked all voltages corresponding to the analog inputs such
as Vdda and Vssa and their values are OK.
> Any suggestions and ideas are
> Georg Bende
> Abteilung Elektronik
> Dr. Fritz Faulhaber GmbH & Co
> Daimlerstr. 23
> 71101 Schaich
> Tel: +49 7031 638294
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