Reply by Wayne Radochonski●February 10, 20052005-02-10
Bob, et al.
Thanks again to everyone who responded to my query...
Wayne
Bob_xyz <> wrote:
A fairly low-value resistor is sometimes placed in series with a 32
KHz crystal to reduce the drive level. Most 32 KHz crystals don't
require (and some can't tolerate) as much drive as higher frequency
crystals usually do. If the processor has a configuration setting to
reduce the level (like the PIC micros do), the series resistor is
usually omitted.
Regards, Bob
--- In , "dharmaBum" <dharmabum@y...> wrote: >
> If anyone has successfully used a 32 KHz crystal with the LPC2138,
> please explain how to connect the crystal.
>
> I saw an example on the Keil eval board where a resistor was
> connected in series with the crystal. I don't understand how that
> circuit operates.
>
> Generally, a 10M or other large resistor is connected in parallel
> with a crystal in order to bias the oscillator buffer (inside the
> uP) into its linear region.
>
> Has Philips released a more complete data sheet or user manual?
>
> Thanks for the help,
> Wayne Radochonski
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A fairly low-value resistor is sometimes placed in series with a 32
KHz crystal to reduce the drive level. Most 32 KHz crystals don't
require (and some can't tolerate) as much drive as higher frequency
crystals usually do. If the processor has a configuration setting to
reduce the level (like the PIC micros do), the series resistor is
usually omitted.
Regards, Bob
--- In , "dharmaBum" <dharmabum@y...> wrote: >
> If anyone has successfully used a 32 KHz crystal with the LPC2138,
> please explain how to connect the crystal.
>
> I saw an example on the Keil eval board where a resistor was
> connected in series with the crystal. I don't understand how that
> circuit operates.
>
> Generally, a 10M or other large resistor is connected in parallel
> with a crystal in order to bias the oscillator buffer (inside the
> uP) into its linear region.
>
> Has Philips released a more complete data sheet or user manual?
>
> Thanks for the help,
> Wayne Radochonski
Reply by Onestone●February 10, 20052005-02-10
I don't know why you say 'generally'. This is micro specific
(especially
moto parts). PICs, MSP430 etc etc don't need this.
I would asusme that a dedicated RTC crystal oscillator would, like the
MSP430 and others, already be matched for a typical watch crystal. Most
6pF load capacitiance watch crystals should then work by directly
connecting them, no load caps, no resistors.
Al
dharmaBum wrote:
>
> If anyone has successfully used a 32 KHz crystal with the LPC2138,
> please explain how to connect the crystal.
>
> I saw an example on the Keil eval board where a resistor was
> connected in series with the crystal. I don't understand how that
> circuit operates.
>
> Generally, a 10M or other large resistor is connected in parallel
> with a crystal in order to bias the oscillator buffer (inside the
> uP) into its linear region.
>
> Has Philips released a more complete data sheet or user manual?
>
> Thanks for the help,
> Wayne Radochonski
> >.
>
>
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Reply by dharmaBum●February 10, 20052005-02-10
If anyone has successfully used a 32 KHz crystal with the LPC2138,
please explain how to connect the crystal.
I saw an example on the Keil eval board where a resistor was
connected in series with the crystal. I don't understand how that
circuit operates.
Generally, a 10M or other large resistor is connected in parallel
with a crystal in order to bias the oscillator buffer (inside the
uP) into its linear region.
Has Philips released a more complete data sheet or user manual?