On 30/04/2011 08:58, Wouter van Ooijen wrote:
> In a 12C509 cicruit (for which I try to find out what the fuses setting
> should be) the crystal is connected between OSC1 and ground (without any
> capacitors). Is this a working way to connect a crystal? (and if so,
> what should be the config setting?)

Any PICs I used have Crystal part of a feedback circuit. But my little=20
crystal checker uses a crystal to ground, such a circuit is feasible.

Any schematics I see of 12C509 use pin 2 &3 and this seems to be=20
suggested by data sheet.
http://www.oocities.org/uirr/index.htm
http://wb9kzy.com/markr509.zip

but it's not impossible that there is configuration to allow what you=20
suggest and release a pin for I/O. Read datasheet this doesn't seem to exis=
t

bit  1-0: FOSC1:FOSC0: Oscillator selection bits
11 =3D EXTRC - external RC oscillator
10 =3D INTRC - internal RC oscillator
01 =3D XT oscillator
00 =3D LP oscillator


see page 26 of datasheet. Only Series Resonator or Crystal between pin2=20
& 3 is shown, with optionally a series resistor on drive pin to crystal.

R C oscillator of course only uses Ckin pin with C to ground. It might=20
be possible to get "some" crystal to work in the RC mode? If there is=20
really a crystal on pin to ground and this works, it must be in mode 11=20
=3D EXTRC - external RC oscillator as this uses internal feedback and=20
external RC, so could conceivably work. Modes 01 and 00 use crystal or=20
resonator between two pins. Mode 10 doesn't use anything external.




--=20
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