Re: SPI problem
- From: "MK" <nospam@xxxxxxxxxxxxx>
- Date: Thu, 15 Jan 2009 16:54:59 -0000
"mahesh.himane" <mahesh.himane@xxxxxxx> wrote in message
news:UpedncbQj9Yv_vLUnZ2dnUVZ_q3inZ2d@xxxxxxxxxxxxxxx
I am using MPC5200 processor and ADC chip ADS7927. These are connected with
SPI interface with frequency of 16MHz. the track length is large that is
around 10cm. I am facing the basic problem some thing about the loading.
When I am connecting probe to the SCK line on the ADC then I am getting
correct result from ADC, whereas if I remove DSO probe from SCK line then
junk data is readed from ADC.
This is definatly the loading problem. please provide the solution how to
solve the problem. Should adding pullup on the SCK line will help? Or
should I use some other termination method?
Don't be so sure that this is a loading/termination problem. I have seen SPI
with the phase settings wrong but still working if loaded with scope or
capacitor.
If you are sure that the settings are correct then use your scope to tell
you what is wrong with the signals (you might need to make yourself a low
capacity probe with a couple of surface mount resistors). You'll know when
you have got the probe right - it won't make the ADC work any more and when
you connect a second probe on the SAME signal it won't change (much).
Once you know what is wrong with your signals you might be able to fix them.
(Or if it's a one off and you are in a hurry just look up the scope probe
capacitance in the manual and add a little capacitor to earth (and don't
tell anyone I suggested it))
Michael Kellett
.
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