piclist 2000\11\04\192802a >
Thread: Bug in LTC2400 SPI interface
face BY : Dan Michaels email (remove spam text)


>>a) RC filter in the sclk line at the A/D - 330 ohm, 27 pF.
>Try impedance matching the sender instead: putting an resistor in series
with the driver of equal resistance as the line impedance, makes the
incident wave travelling down to the reciever have half the voltage step,
but the moment it reaches the reciever it is full step.

That is in there too.

>>c) placing finger on the A/D SPI pins - [not field-installable].
>Mix some carbon dust with rubber mixture and pour over...?
>(joke of course)

Got to be either R(finger) or C(finger) - I doubt my finger has
much inductance.

{Quote hidden}

Alright - turns out after making my first post to your problem,
I went back and looked at my Scenix code. Sclk changes exactly
33.33nsec after Conv - far less than 80nsec. Add in a little
capacitance in the 7mm track, and ---> flaky ops. I now see that
the behavior I was observing was related to when the 1st bit was
sensed by the Scenix.

Your problem reminded me of the timing thing - which I had obviously
forgotten when I wrote the code. Haven't tried it yet, but I am sure
this is the problem.

Thanks for finding my error :-).
- danM

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See also: www.piclist.com/techref/io/serial/spis.htm?key=spi
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Subject (change) Bug in LTC2400 SPI interface

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