Author Topic: crystal oscillator instead of crystal  (Read 6624 times)

Rons

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crystal oscillator instead of crystal
« on: June 20, 2005, 12:39:34 pm »
I was using a 30MHz crystal and 2 27pf capacitors on a 80C51 XA.
I noticed that sometimes the clock frequency was 10MHz depending on
how I bypassed the clk1 & clk2 pins.  Replacing a 2 pin 30Mhz crystal with a 30MHz crystal oscillator (4 pin) madequite a big difference in baud rate.
 I used to get no higher than 38,400 with just a crystal and two 27pf capacitors.  But now I can send and receive at 115200. The quality of the
clock signal makes a difference.

erikm

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Re: crystal oscillator instead of crystal
« Reply #1 on: June 20, 2005, 02:05:37 pm »
I was using a 30MHz crystal and 2 27pf capacitors on a 80C51 XA.
I noticed that sometimes the clock frequency was 10MHz depending on
how I bypassed the clk1 & clk2 pins

wrong forum.  Oh well, you used an overtone crystal instead of a fundamental crystal, that's why.

Erik

Rons

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Re: crystal oscillator instead of crystal
« Reply #2 on: June 21, 2005, 11:34:11 am »
>I noticed that sometimes the clock frequency was 10MHz depending on
>how I bypassed the clk1 & clk2 pins
>wrong forum. Oh well, you used an overtone crystal instead of a f>undamental crystal, that's why.

If you leave a cap on pin XTAL2 but remove the cap on XTAL1 you
will not get a resonance of 30M, put the cap on XTAL1 and get 10M.

erikm

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Re: crystal oscillator instead of crystal
« Reply #3 on: June 21, 2005, 12:32:29 pm »
If you leave a cap on pin XTAL2 but remove the cap on XTAL1 you
will not get a resonance of 30M, put the cap on XTAL1 and get 10M.

Incorrect, replace "if you" with "by luck when I"
There is no way in hades to get overtone crystals to behave predicatably with a XA/'51

Erik