question about microcontroler oscillator

[robb]

saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave out
of one side and a very bad dent in the crest of the sine wave on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave ?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps which
connect to 0v ref


thanks for any help,
robb

 

[Don McKenzie]

robb wrote:

saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave out
of one side and a very bad dent in the crest of the sine wave on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave ?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps which
connect to 0v ref


thanks for any help,
robb

doesn't sound like a good waveform for micro operation.

http://www.intel.com/design/mcs51/applnots/23065901.pdf
have a look at page 13, this is what the original data sheets specify
for 8051's.

Don...




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Serial OLED uses standard micro-SD memory cards.
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[Eeyore]

robb wrote:

saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave out
of one side and a very bad dent in the crest of the sine wave on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave ?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps which
connect to 0v ref

What value are the caps ? I think you mean you have a ceramic resonator btw, not
an oscillator.

Graham

 

[Pieter]

On Mon, 29 Oct 2007 16:42:11 -0500, "robb" <some@where.on.net> wrote:

saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave out
of one side and a very bad dent in the crest of the sine wave on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave ?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps which
connect to 0v ref


thanks for any help,
robb

Hi,

Make sure your scope probe is set to 10x, and has a low capacitance.
The probe may have more capacitance tha the small capacitors near the
crystal (10 pF?) and may load the signal. So you may be measuring what
it does when you load it with a capacitor.

Regards,
Pieter

 

[robb]

"Pieter" <dit3_werkt_ook_niet@hotmail.com> wrote in message
news:ngsci3t2oho8h1ouf4imcrd5ndsoqreo0g@4ax.com...

On Mon, 29 Oct 2007 16:42:11 -0500, "robb" <some@where.on.net
wrote:

saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock
signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave
out
of one side and a very bad dent in the crest of the sine wave
on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave
?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps
which
connect to 0v ref


thanks for any help,
robb



Hi,

Make sure your scope probe is set to 10x, and has a low
capacitance.
The probe may have more capacitance tha the small capacitors
near the
crystal (10 pF?) and may load the signal. So you may be
measuring what
it does when you load it with a capacitor.

Regards,
Pieter

Thanks Pieter,
I was planning to post pics of the wave forms on
"alt.binaries.schematics.electronic"
in case i am not describing correctly or if it helps someone,
help me, figure out if i am seing the correct thing.

i just read about intel's specs on the "oscillator for
microcontrollers" and my head is spinning { loading, gain, drive,
tolerance, reactance, optimal loading ...} they described using a
*MOSFET buffer* to view the signals on o-scope and setting to
vertical AC measurement which seems to address the problem you
were alluding to.

so i will try to verify i am not measuiring my loading if that
majkes sense.
my probes are the tek 10x 6109B (~12 pF)

thanks for help,
robb

 

[Eeyore]

robb wrote:

"Eeyore" wrote

What value are the caps ? I think you mean you have a ceramic
resonator btw, not an oscillator.

thanks for help Graham,

the values for caps (grey w/black top) are 15p and 33p

after reading the intel oscillator spec i expected them to be the
same value but then maybe i missed something (well, alot)

I'd expect them to be the same value too (and about 30pF typically - check the
resonator data sheet). See any 8051 application note too. Is the 8051 version
you're using CMOS btw ?

Graham

 

[robb]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:4726700D.87B64BF8@hotmail.com...

robb wrote:

while trying to isolate trouble with a badly shaped clock
signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave
out
of one side and a very bad dent in the crest of the sine wave
on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave
?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps
which
connect to 0v ref

What value are the caps ? I think you mean you have a ceramic
resonator btw, not
an oscillator.

thanks for help Graham,

the values for caps (grey w/black top) are 15p and 33p

after reading the intel oscillator spec i expected them to be the
same value but then maybe i missed something (well, alot)

thanks for help/reply,
robb

 

[robb]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:4726AE91.4728881F@hotmail.com...

robb wrote:

"Eeyore" wrote

What value are the caps ? I think you mean you have a
ceramic
resonator btw, not an oscillator.

thanks for help Graham,

the values for caps (grey w/black top) are 15p and 33p

after reading the intel oscillator spec i expected them to be
the
same value but then maybe i missed something (well, alot)

I'd expect them to be the same value too (and about 30pF
typically - check the
resonator data sheet). See any 8051 application note too. Is
the 8051 version
you're using CMOS btw ?

Graham

the (phillips 8051ah)

datasheet says +5v depletion-load,N-chanel,silicon-gate,N500 MOS

so my slight comprehension leads me to "yes ?"

i am having difficulty finding the resonator datasheet which is
why i am troubling "s.e.b"
my reliable finds come from alldatasheet.com but not for the
resonator

thanks for help Graham,
robb

 

[Lostgallifreyan]

"robb" <some@where.on.net> wrote in
news:13id020fnftjh6c@corp.supernews.com:

they described using a
*MOSFET buffer* to view the signals on o-scope

I was thinking of that before I saw it. Look at the thread above this one
called "Search OpAmp chip as a voltage follower" for a description of using
a FET to buffer a high impedance source. That same idea will let you get a
look at that waveform without disturbing it much. The FET and a single
resistor to a stable DC rail should be all you need, then scope the FET
output signal.

FET input op-amp as non-inverting unity gain buffer might also be enough,
and more likely to be close at hand.

 

[TT_Man]

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns99D975BD17ABAzoodlewurdle@140.99.99.130...

"robb" <some@where.on.net> wrote in
news:13id020fnftjh6c@corp.supernews.com:

they described using a
*MOSFET buffer* to view the signals on o-scope

I was thinking of that before I saw it. Look at the thread above this one
called "Search OpAmp chip as a voltage follower" for a description of
using
a FET to buffer a high impedance source. That same idea will let you get a
look at that waveform without disturbing it much. The FET and a single
resistor to a stable DC rail should be all you need, then scope the FET
output signal.

FET input op-amp as non-inverting unity gain buffer might also be enough,
and more likely to be close at hand.
If you are seeing 3-4 volts swing on one of the pins, then I would say the

resonator is working ok. Don't worry too much about the wiggle in the
waveform.

 

[Eeyore]

robb wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote

I'd expect them to be the same value too (and about 30pF
typically - check the resonator data sheet). See any 8051 application note
too. Is
the 8051 version you're using CMOS btw ?

the (phillips 8051ah)
datasheet says +5v depletion-load,N-chanel,silicon-gate,N500 MOS

so my slight comprehension leads me to "yes ?"

No, that's not a CMOS part and I'm puzzled why you're using it. Is this some old
piece of equipment ?

i am having difficulty finding the resonator datasheet which is
why i am troubling "s.e.b"

Where do you buy it from ? The "CSA 12.00 MT" marking is the same as ones I've
sourced from Farnell (Murata ?) and works fine with 2 x 33pF.

Graham

 

[Eeyore]

Lostgallifreyan wrote:

"robb" <some@where.on.net> wrote

they described using a
*MOSFET buffer* to view the signals on o-scope

I was thinking of that before I saw it. Look at the thread above this one
called "Search OpAmp chip as a voltage follower" for a description of using
a FET to buffer a high impedance source. That same idea will let you get a
look at that waveform without disturbing it much. The FET and a single
resistor to a stable DC rail should be all you need, then scope the FET
output signal.

A FET input probe is NOT required to look at the 8051oscillator for routine
purposes. A 10x probe is fine.

Graham

 

[Eeyore]

TT_Man wrote:

If you are seeing 3-4 volts swing on one of the pins, then I would say the
resonator is working ok. Don't worry too much about the wiggle in the
waveform.

Yes, it'll be around 3-4 V pk-pk on one pin (Osc 2 ?) and about a couple of
hundred mV on the other one.

Graham

 

[robb]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:47271F56.FC334B80@hotmail.com...

robb wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote

I'd expect them to be the same value too (and about 30pF
typically - check the resonator data sheet). See any 8051
application note
too. Is the 8051 version you're using CMOS btw ?

the (phillips 8051ah)
datasheet says +5v depletion-load,N-chanel,silicon-gate,N500
MOS

No, that's not a CMOS part and I'm puzzled why you're using it.
Is this some old
piece of equipment ?

Yes, you are correct Graham.
It is the main control board for a vintage "computer controlled"
sewing machine (~25 years old)

i am trying to restore it to functioning ... as a "fun /
learning" electronic hobby project
it has just enough complexity not to completely overwhelm
(hobby-ist) me ;
micro-controller, stepper motors and controls, memory, VFD user
interface and programming buttons etc.....

i am having difficulty finding the resonator datasheet
which is
why i am troubling "s.e.b"

Where do you buy it from ? The "CSA 12.00 MT" marking is the
same as ones I've
sourced from Farnell (Murata ?) and works fine with 2 x 33pF.

it was already on the board.

i was trying to backtrace the CLK signal going to the VFD driver
IC which had some big spikey ring in the leading edges. i was led
back to the 8051 and was checking various pins and noticed warped
? sine waves at the oscillator pins XTAL1 / XTAL2

thanks for your help,
robb

 

[robb]

"TT_Man" <Someone@ntlworld.com> wrote in message
news:s%EVi.723$pg.547@newsfe6-win.ntli.net...

"Lostgallifreyan" <no-one@nowhere.net> wrote in message
news:Xns99D975BD17ABAzoodlewurdle@140.99.99.130...
"robb" <some@where.on.net> wrote in
news:13id020fnftjh6c@corp.supernews.com:

they described using a
*MOSFET buffer* to view the signals on o-scope

I was thinking of that before I saw it. Look at the thread
above this one
called "Search OpAmp chip as a voltage follower" for a
description of
using
a FET to buffer a high impedance source. That same idea will
let you get a
look at that waveform without disturbing it much. The FET and
a single
resistor to a stable DC rail should be all you need, then
scope the FET
output signal.

FET input op-amp as non-inverting unity gain buffer might
also be enough,
and more likely to be close at hand.
If you are seeing 3-4 volts swing on one of the pins, then I
would say the
resonator is working ok. Don't worry too much about the wiggle
in the
waveform.

Thanks for reply,
that is what i see about 4 volts height on wave forms on both
pins . One is slightly bent sine wave the other has a big dent in
the wave

thanks for help
robb

 

[robb]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:47271FD7.53D44280@hotmail.com...

TT_Man wrote:

If you are seeing 3-4 volts swing on one of the pins, then I
would say the
resonator is working ok. Don't worry too much about the
wiggle in the
waveform.

Yes, it'll be around 3-4 V pk-pk on one pin (Osc 2 ?) and about
a couple of
hundred mV on the other one.

well i am seeing about 4 volts on one side (the 33 pF side)
and about 3.8 volts on the (15pF) side ?

so does that mean i have a problem ?

this 8051 chip supposedly has and internal oscillator ? why would
that not be used ?
i mean is there a reason one would not use internal oscillator if
there were one.

thanks for all the help everyone, it helps me learn,
robb

 

[Eeyore]

robb wrote:

i was trying to backtrace the CLK signal going to the VFD driver
IC which had some big spikey ring in the leading edges. i was led
back to the 8051 and was checking various pins and noticed warped
? sine waves at the oscillator pins XTAL1 / XTAL2

From memory, yes they are a bit 'warped' as you put it. They're certainly not
clean square waves. I wouldn't worry about it.

Graham

 

[Eeyore]

robb wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
TT_Man wrote:

If you are seeing 3-4 volts swing on one of the pins, then I
would say the resonator is working ok. Don't worry too much about the
wiggle in the waveform.

Yes, it'll be around 3-4 V pk-pk on one pin (Osc 2 ?) and about
a couple of hundred mV on the other one.


well i am seeing about 4 volts on one side (the 33 pF side)
and about 3.8 volts on the (15pF) side ?

so does that mean i have a problem ?

I doubt it. It expect it's simply different to the usual 80C51 CMOS version that
I'm familiar with. That NMOS version must be VERY old.

this 8051 chip supposedly has and internal oscillator ? why would
that not be used ?

It IS being used. That's what the XTAL1 and XTAL2 pins are for. See any 8051
datasheet.

Graham

 

[Lostgallifreyan]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote in
news:47271F9B.673DD522@hotmail.com:

Lostgallifreyan wrote:

"robb" <some@where.on.net> wrote

they described using a
*MOSFET buffer* to view the signals on o-scope

I was thinking of that before I saw it. Look at the thread above this
one called "Search OpAmp chip as a voltage follower" for a
description of using a FET to buffer a high impedance source. That
same idea will let you get a look at that waveform without disturbing
it much. The FET and a single resistor to a stable DC rail should be
all you need, then scope the FET output signal.

A FET input probe is NOT required to look at the 8051oscillator for
routine purposes. A 10x probe is fine.

Graham

Didn't say it was necessary. So long as the wave crosses the zero point
regularly enough to make the timer work who cares what shape it is? Nothing
much routine about this anyway, the guy's new to it and wants to be sure of
what he sees.

I was just pointing out a useful similarity with another post. If someone
wants to learn, there's no doubt that adding a FET and a resistor and a DC
cource is a neat way of making sure a signal involving small capacitances
might be less disturbed than by loading it directly with a cable
connection. It's not a question of whether it's necessary, but whether or
not it's useful. Robb wants to learn, so that's a good cheap way to do it.
It would confirm that the waveform really is as he sees it, and that it's
not being changed by his connection to it.

 

[LVMarc]

robb wrote:

saga continues,
my repair project device uses a phillips MAB 8051 AH
microcontroller.

while trying to isolate trouble with a badly shaped clock signal
i happened across microcontroller oscillator.

the oscillator CSA 12.00 MT has a slightly warped sine wave out
of one side and a very bad dent in the crest of the sine wave on
the other side like...
_
/ \__
/ \
-/------------\

is the output of the oscillator suppose to be clean sine wave ?
and same on both sides ?

oscillator is connected exactly as 8051 datasheet recommends,
with the two pins from the oscillator each to small caps which
connect to 0v ref


thanks for any help,
robb



problem with most probed uP oscillator studies, is:

the capacitance of the probe is about the same as capactiane of the
oscillator,

so like hiesenberg, when you look a the clock, you effect it by looking
with the probe. try a non contact probe and then see the real clock
output shape(but not the corectd amp,itude), to get amplitude you need
to correct the raw non contact data and rescale to measure the amplitude.

Good luck with the measurent

marc