[oopic] Re: DDELink bug and linking 2 Oopic Rs

--- In oopic@yahoogroups.com, ooPIC Tech Support <dennis.clark@...>
wrote:
>
> One other thing - The problem does not exist when using ooPIC II+
chips,
> ooPIC II or any other ooPIC version on ooPIC S boards. It ONLY
happens
> when using an ooPIC R or ooPIC C, which use the QFP packages, and
are
> 16F877a chips.
>
> DLC
>

Well, that is interesting. I think the OOBoard also uses the smt
parts. Do you know if it also has the problem?

> dan michaels wrote:
> > --- In oopic@yahoogroups.com, ooPIC Tech Support <dennis.clark@>
> > wrote:
> >
> >>I've played with this problem for off and on for a while it seems
> >
> > and
> >
> >>can't find any good explanation or reasoning. You should be
using
> >
> > 2.7K
> >
> >>to 4.7K for even short distances (measured in single digit
> >
> > centimeters)
> >
> >>but it simply won't work between any two ooPICs that use the
> >
> > 16F877a
> >
> >>processor and I just don't understand why.
> >
> >
> >
> >
> > I've never played with DDE, but this large resistor value
business
> > makes no sense, as the 877(A) pins can all source and sink
upwards to
> > 20-mA. 5v/20mA = 250 ohms!
> >
> > I wonder if there isn't some problem with the code on the newer
> > firmware not switching modes properly between output and input,
ie
> > some timing issue, when the data transfers switch direction.
> >
> > JFTHOI, you might try putting a small series R in the leads
between
> > the 2 OOPic 2+ chips and see if that helps. Just a shot in the
dark.
> >
> >
> >
> >
> > Putting an ooPIC S board in
> >
> >>the circuit fixes it, so that left out cable length, noise in the
> >
> > wires
> >
> >>or just bad connectors. If anyone can figure out why this
happens
> >
> > I
> >
> >>offer up a 4 pack of Guiness Draught cans as a prize!
> >>
> >>DLC
> >>
> >>rtstofer wrote:
> >>
> >>>--- In oopic@yahoogroups.com, ooPIC Tech Support <dennis.clark@>
> >
> > wrote:
> >
> >>>>The most certain way to make sure that the DDE link works is to
> >
> > have an
> >
> >>>>ooPIC S in the loop. Otherwise the high value data and clock
> >
> > resistors
> >
> >>>>need to be used. No one can explain this oddity, but it has
> >
> > something
> >
> >>>>to do with the PIC 16F877a part.
> >>>>
> >>>>DLC
> >>>
> >>>
> >>>If you have to use 22k to 33k resistors, the cable length
between
> >
> > the
> >
> >>>OOPics will have to be measured in small numbers of inches.
That
> >
> > much
> >
> >>>resistance just won't overcome any kind of capacitance.
> >>>
> >>>A conventional I2C network would have resistors in the 2.2k
range.
> >>>
> >>>Unfortunately, I only have a couple of S boards so I can't
really
> >
> > test
> >
> >>>the bug to see what is happening.
> >>>
> >>>Richard
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>Yahoo! Groups Links
> >>>
> >>>
> >>>
> >>
> >>--
> >>------------------------------------------------------
> >>Dennis Clark ooPIC Tech Support
> >>www.oopic.com
> >>------------------------------------------------------
> >>
> >
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
>
> --
> ------------------------------------------------------
> Dennis Clark ooPIC Tech Support
> www.oopic.com
> ------------------------------------------------------
>

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