At 09:31 PM 5/15/06 +0300, Vasile Surducan wrote:
>On 5/15/06, Spehro Pefhany <speff@interlog.com> wrote:
> > ... long list of chips
> > to which a fix is required to recognize the falling edge of /SS.
> >
> > http://ww1.microchip.com/downloads/en/DeviceDoc/80131d.pdf
> >
> > The question..
> >
> > It should (I think) work with /SS enabled and simply grounded, but I do=
n't
> > see that happening. But with it grounded through a resistor (!) it does
> > seem to work. Can anyone confirm this mode is buggy as all git out?
>
>This is a great erata:
>
>" Work around
>Insert a series resistor between the source of the
>SS signal and the corresponding SS input line of
>the microcontroller. Start with a 1 k=A7=D9 resistor and
>increase the value as necessary until the SS pin
>edge is recognized. A fall time of a few nanoseconds
>should be sufficient. The value of the
>resistor is dependent on both the application
>system's characteristics and process variations
>between microcontrollers. ****Experimentation and
>thorough testing is encouraged****.
>This is a recommended solution. Others may exist."
>
>The parasitic capacitance of input PIC pin is about 5...7pF.
>Maybe sensing the edge is based on 1K * 7pF delay ?
>
>Vasile

Omigod...I thought you made that up!  Then I read the errata.
I noticed that /SS can also be programmed as an analog pin.  But we
would never make a mistake like that :-)

This reminds me of working on my first SPI interface with PIC's.  But that
message would deserve its own thread title.

Barry


-- =

http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist