Lpc2000

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

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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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 lpc2000@yahoogroups.com, "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

Bob, et al.
 
Thanks again to everyone who responded to my query...
 
Wayne

Bob_xyz <bob_barr@...> 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 lpc2000@yahoogroups.com, "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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