Maker Pro
Maker Pro

8051 does not oscillate

C

ClueLess

Jan 1, 1970
0
Hi 8051 experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

Thanks for your time and attention

ClueLess
 
M

Mike Silva

Jan 1, 1970
0
Hi 8051  experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

Thanks for your time and attention

ClueLess

If your wiring and uC oscillator configuration correct then my guess
is that either you've installed a damaged part, or perhaps the
breadboard layout had extra capacitance that your PCB does not have,
and that your oscillator needs to start up.
 
Hi 8051 experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

Thanks for your time and attention

ClueLess

the best way to debug a circuit, be it analog or digital, is to
identify few important nodes and verfiy their voltage values (both
calculated and observed values must be equal). but digital circuits
are easier to follow coz voltage value is either 0 or somewhere near
5V. so whenever there is a mismatch, try get the required voltage at
the node by tracing the problem from its output........... so u have
solved it.............
 
Hi 8051 experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

Thanks for your time and attention

ClueLess

a mere multimeter will suffice to debug the problem..........
 
J

Jamie

Jan 1, 1970
0
ClueLess said:
Hi 8051 experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

Thanks for your time and attention

ClueLess
You need to add capacitance.!



http://webpages.charter.net/jamie_5"
 
E

Eeyore

Jan 1, 1970
0
ClueLess said:
Hi 8051 experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

What value caps are you using around the crystal ?

Graham
 
J

Joerg

Jan 1, 1970
0
ClueLess said:
Hi 8051 experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

Thanks for your time and attention

As others have pointed out it could be your layout. Best is to post the
layout and if you can, also the schematic.

Do you have a full ground plane on that board?
 
A

Allen Bong

Jan 1, 1970
0
Hi 8051  experts there

I have made a circuit for remote switching of or on a motor using
89C2051 and the program has checked out in the emulator. Also I have
put the whole thing on a breadboard a hundred times and it has worked
every time as expected without any flaw.

But when I made PCB, soldered all the parts and power it on it does
not work - the crystal fails to oscillate. I have in fact taken the
same components that form the crystal circuit after successful test to
the PCB it still fails.

I have checked the PCB for any errors and also discontinuity for any
breaks - I could find none.

And the crystal is just a slow one, 32.768 kHz clock crystal, that
works without a hitch on the breadboard.

This is just baffling me. Can any of you suggest what else I should
look for?

Thanks for your time and attention

ClueLess

Try with a higher freq xtal say 6MHz and see it oscillates. If it
does, then you need to add capacitance.

Allen
 
C

ClueLess

Jan 1, 1970
0
What value caps are you using around the crystal ?

It is really gratifying to see the number of responses to my query -
the suggestions have really given me a number of leads to test
further.

32.786 crystal, according to literature, needs 11 pf capacitors but I
found this did not work and I had to use either 22 or 33 pf capacitors
to get it work on the breadboard.

I removed the crystal and capacitors from the pcb and connected pins
X1 and X2 of 8051 direct to the breadboard - it works.

On the breadboard everything is widely spaced but on the pcb they are
very close. So it could be a layout problem. I have redesigned the pcb
isolating the crystal circuit from the other parts, added more space
between pads and also added a ground plane under the crystal parts. I
will get the board made and come back after trying it.

And thanks again to all of you for your time and attention

Thanks for your time and attention

ClueLess
 
R

Rich Grise

Jan 1, 1970
0
On Sat, 29 Mar 2008 16:48:17 +0000, Eeyore


It is really gratifying to see the number of responses to my query -
the suggestions have really given me a number of leads to test
further.

32.786 crystal, according to literature, needs 11 pf capacitors but I
found this did not work and I had to use either 22 or 33 pf capacitors
to get it work on the breadboard.

I removed the crystal and capacitors from the pcb and connected pins
X1 and X2 of 8051 direct to the breadboard - it works.

On the breadboard everything is widely spaced but on the pcb they are
very close. So it could be a layout problem. I have redesigned the pcb
isolating the crystal circuit from the other parts, added more space
between pads and also added a ground plane under the crystal parts. I
will get the board made and come back after trying it.

And thanks again to all of you for your time and attention

Thanks for your time and attention

I hate to nag, but you _did_ include the caps in your layout, didn't
you? If you've got, say, 2x 22 pf and it still doesn't start, you
might try changing the ratio of capacitances (as long as the series
connection still comes out at 11 pf) to diddle with the drive and
feedback.

Good Luck!
Rich
 
C

ClueLess

Jan 1, 1970
0
I hate to nag, but you _did_ include the caps in your layout, didn't
you? If you've got, say, 2x 22 pf and it still doesn't start, you
might try changing the ratio of capacitances (as long as the series
connection still comes out at 11 pf) to diddle with the drive and
feedback.

Hi Rich

That was the first thing I did, put two 22s in series to get 11 pf and
try. All data on 32.786 kHz crystals said 11pf but the dozen crystals
I had insisted on either 22 or 33 pf

I feel that it is the layout, I am just waiting for the new board,
expected Friday when I will stuff it and see where it goes.

Thanks for your time

Thanks for your time and attention

ClueLess
 
Top