question about microcontroler oscillator

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

The 8051 does not have an internal oscillator. But the chip is very reliable and does not often give oscillation problems. You could check the board for decoupling problems, that may influece things.

Pieter

What do you mean ? It has an inverter stage designed for clock oscillator use connected to pins xtal1 and xtal2.

Graham

out

on

work? Have

thanks for reply, good question, functions somewhat but not acceptable, so no , there seems to be some sluggishness in the response to user button presses, sometimes missed presses, sometimes multiple presses are registered

the short is there appears to be a problem but nothing is predictably repeatable .... so, i began looking at the most immediate source of trouble with button presses and found that the clock signal was malformed with ringing 1-2 volts out before settling about 1/3 accross square (pic of signal posted in "alt.binaries.schematic.electronics" )

so following the circuit to the clock source led me back to 8051 and i am still trying to deteermine where the problem with ringing is coming from

This is learning exercisize as i am amateur electronics troubleshooter

i will check how reset pin is connected

thanks for help, robb

about

would

if

very

could check

thanks for help Pieter,

everytime i read your posts i feel like a professor has given me a research assignment so now to read up un decoupling :)

thanks robb

above this

source. That

disturbing

should be

zero point

is? Nothing

to be sure of

you have pegged it exactly with just wanting peace of mind and some learning experience

i could be reading forever.... sometimes you just have to get in and do it to learn which id what i am doing.

If someone

resistor and a DC

capacitances

cable

whether or

way to do it.

that it's

and that is exactly what i plan to do (build a mosfet buffer that is) because it sounds interesting, useful and fun and good way to learn

as long as i do not blow up my project in the process.

right now i am at the point of just check everything big and question anything unexpected.

thanks for all the help,

robb

signal

out

on

which

the

looking

clock

you need

amplitude.

thanks marc,

i will need to read about non-contct probe , is it something i can make ?? pointy small 30 awg wire wilth tiny loop perhaps ?

thanks again for help, robb

"robb" wrote in news: snipped-for-privacy@corp.supernews.com:

MOSFET. :) That's non-contact, sort of, the gate is insulated. Has capacitance though, but not critical to this.

That's not what was actually meant though, in this case it means a very sensitive input, so sensitive it can pick up the signal without being close enough to load it. Trouble with that is, it might pick up noise from other stuff nearby. I'd go with the FET. Useful tool to keep around.

No internal crystal. It has the inverter etc, but always needs an external crystal. Of course you can also feed it with an external oscillator.

Regards, Pieter

Check the decoupling capacitors.

Pieter

Are you using Port 0? Do you have pull-ups on all the pins on Port 0? That's a common beginner mistake.. Without them, strange illogical things happen.....

Can you provide an example of any IC that has an internal crystal ?

Graham

It's not HIS design. It's a commercial one.

Graham

Not crystals, but many of the small microcontrollers have trimmed RC oscillators internally, allowing them to be used for 'low accuracy' applications, without any external oscillator. There have been a couple of hybrid chip modules marketted in the past with crystals included, but I don't know if any currently offer this.

Best Wishes

Sure:

I'd love to know how he's going to CHECK capacitors ! You certainly say some daft things.

He might REPLACE any supply decoupling caps that are electrolytic types for sure. Age is likely to have taken their toll on them.

Graham

use

Yes, I'm aware of that. To be honest, I'm being critical of Pieter who is introducing pointless irrelevancies.

Exactly, hybrids not ICs. A very distinct difference that you for one are aware of.

Graham

Whilst the data sheet doesn't make it obvious, that's a HYBRID, not an IC.

Graham

So what? The point is that some parts have internal oscillators, not just the inverters etc for external crystals, resonators or RC's. Microchip etc.

Pieter