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
> ------------------------------------------------------
>
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