Hi Charlie,
--- In "charliem_1216" <>
wrote:
>
> Hi --
>
> --- In "j.chitte" <j.chitte@> wrote:
> >
> > Hi,
> >
> > the sample code in adc_7250.c shows how to control the five ADC
> > channels on the std 7250.
> >
> > Where is the documentation relating to use of the optional extra
8
> > channels?
>
> The 8 channels are in the optional MAX197 chip, and the data sheet
> is available from Maxim. This data sheet, the TS example code,
and
> the device driver in the files section of the forum should be
plenty
> of documentation.
Yes that group of resources should help. An explicit reference to the
MAX197 as part of the spec sheet for the 7250 may have helped me
realise what max197.pdf refered to.
Also I dont see the driver tarball on ftp://ftp.embeddedarm.com/
downloads , that seems on odd ommission if I need to disect it to get
essentials like how access the device. It should not be left to an
unofficial use group.
Anyway thanks for the pointer. The example file in the tarball seems
to be what I was looking for.
>
> [FYI, your board must be ordered with the MAX197 chip, it cannot
be
> added after the fact unless the board is reprogrammed by TS.]
>
> >
> > also the example following line relating to converting the ADC
> input
> > data but there is no comment as to why this is needed or the
> meaning
> > of the 0x7000 test.
> >
> > if(avg < 0x7000)
> > avg = avg + 0x10000;
> >
> > Neither do I see anything in the Cirrus data sheet that would
> explain
> > this.
>
> First, this only applies to the 5 built-in A/D channels on the
> cirrus chip, not the MAX197.
>
> To see why it's needed, look at the transfer function (digital
> output vs. analog input voltage) on p.34 of the EP9302 Data
Sheet.
> See how the digital output rolls over from 0xFFFF to 0x0000 around
> (Vref / 2)? Replot the line, with input voltage on the Y-Axis,
and
> digital output on the X-axis (0x0 to 0xFFFF), and it's a little
> clearer. The 0x10000 is essentially shifting one section of the
> curve so the output is a single line not two saw-teeth.
thanks for the explaination , that makes more sence. A comment in the
example would help make this oddity more transparent. After all , the
example code is there to explain , not to just work, and this quirk
is less than obvious.
However, I dont see this in the reference.
http://www.embeddedarm.com/downloads/Components/EP9302-PP2.pdf
Here I see a straight line tranfer function in fig20 on page 32. What
document are you refering to?
Is this example a hangover from an earlier board perhaps?
Thanks again for your help. ;)
>
> >
> > Can anyone shed any light of this?
> >
> > TIA
> >
>
> Regards, ........ Charlie
>
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