Truncated match.
PICList
Thread
'QRe: tapping xtal oscillator'
1999\08\28@114011
by
Anne Ogborn
|
Dave VanHorn wrote:
>
> > The obvious thing to do is to tap into the xtal output.
> > So, can somebody tell me what sort of electronic wizardry I have
> > to do to make the 4MHtz crystal drive some sort of gate so I can
> > divide by 4 and drive the ISD chip???
>
> Careful.
>
> Check the spec, there should be an output drive spec for that pin. If not,
> you're in shaky territory, no matter how many hobby projects or protos "just
> worked". The most interesting part of a data sheet is often what is NOT in
> it.
>
Thanks - I'm with you, that it worked in the prototype means nothing. Otherwise
I'd stick a part in the breadboard and have an answer in the same time I could e
mail.
Buuuuut.......
this means I have to *understand* this circuit.
Well, found something interesting -
To quote the uChip data sheet:
OSC2 - Oscillator Crystal output. Connects to crystal or resonator in
crystal oscillator mode. In RC mode, OSC2 pin outputs CLKOUT which has 1/4 the
frequency of OSC1, and denotes the instruction cycle time.
OK - if I can find a reasonable price can oscillator, I don't need the divide by
4
chip. That might justify some/all of the can's price.
> and the eng mgr told me that all the protos
> worked, and "don't worry.." Guess who got to fly to kaohsiung christmas
> day to debug an assembly line full of product that didn't run... :(
Uhhh.... let me guess. It was the eng mgr? Right? No??? Did he happen to have po
inty hair?
--
Anniepoo
Need loco motors?
http://www.idiom.com/~anniepoo/depot/motors.html
1999\08\28@141602
by
Bob Drzyzgula
On Sat, Aug 28, 1999 at 08:38:13AM -0700, Anne Ogborn wrote:
>
> OSC2 - Oscillator Crystal output. Connects to crystal or resonator in
> crystal oscillator mode. In RC mode, OSC2 pin outputs CLKOUT which has 1/4 the
> frequency of OSC1, and denotes the instruction cycle time.
I noticed that, too, and it did seem like a way to do
it. But uChip never says anything about Fosc/4 for
anything *but* the RC mode. Does it do this in XT or
HS mode?
--Bob
--
============================================================
Bob Drzyzgula It's not a problem
spam_OUTbobTakeThisOuT
drzyzgula.org until something bad happens
============================================================
1999\08\29@011720
by
Dave VanHorn
|
> Thanks - I'm with you, that it worked in the prototype means nothing.
Otherwise
> I'd stick a part in the breadboard and have an answer in the same time I
could email.
>
> Buuuuut.......
> this means I have to *understand* this circuit.
That's the fun bit. Hanging a track on it connected to a gate isn't JUST
hanging a little extra C on it. It couples in some noise (Remember that
"Route no tracks near the xtal tracks" directive?) and it's a potential EMI
source. The chip you drive better have a nice low Z return to the pic.
Series R would probably help all around, as long as the edges don't get too
fuzzy.
You MIGHT be better with a discrete oscillator, feeding both circuits. A
simple 3 gate HC14 osc can drive a ton, since you aren't needing to tap into
the xtal nodes to do it.
> OSC2 - Oscillator Crystal output. Connects to crystal or resonator in
> crystal oscillator mode. In RC mode, OSC2 pin outputs CLKOUT which has 1/4
the
> frequency of OSC1, and denotes the instruction cycle time.
But can you clock it that fast in RC mode?
> > and the eng mgr told me that all the protos
> > worked, and "don't worry.." Guess who got to fly to kaohsiung
christmas
> > day to debug an assembly line full of product that didn't run... :(
>
> Uhhh.... let me guess. It was the eng mgr? Right? No??? Did he happen to
have pointy hair?
Nope, me.
1999\08\29@064540
by
steveb
> You MIGHT be better with a discrete oscillator, feeding both circuits. A
> simple 3 gate HC14 osc can drive a ton, since you aren't needing to tap into
> the xtal nodes to do it.
Kill two birds with one stone and use a (74HC)4060 which has the
oscillator amp built in (equivalent to PIC HS mode). You get the
oscillator and the divider chain to get clock sources for both
chips.
Steve.
======================================================
Steve Baldwin Electronic Product Design
TLA Microsystems Ltd Microcontroller Specialists
PO Box 15-680, New Lynn http://www.tla.co.nz
Auckland, New Zealand ph +64 9 820-2221
email: .....stevebKILLspam
@spam@tla.co.nz fax +64 9 820-1929
======================================================
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