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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 |
LPC2138 RTC Crystal Connections
Started by ●February 10, 2005
Reply by ●February 10, 20052005-02-10
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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 > >. > > >No virus found in this incoming message. >Checked by AVG Anti-Virus. >Version: 7.0.300 / Virus Database: 265.8.6 - Release Date: 7/02/2005 |
Reply by ●February 10, 20052005-02-10
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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 ●February 10, 20052005-02-10
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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 document.write(''); --------------------------------- Yahoo! Groups Links To --------------------------------- |
