Oscillators

[lpcware]

Content originally posted in LPCWare by coatesm on Thu Oct 07 03:57:02 MST 2010
Hello,

I'm currently a little confused, the user manual for the LPC11xx devices suggests that there are 3 oscillators built into the device, the IRC oscillator, the watchdog oscillator and the system oscillator.  I can't seem to find what frequency the "system oscillator" is?  The "SYSOSCCTRL" register allows us to select a frequency range for this oscillator, and to bypass it, but I cannot find a way of setting the frequency to a known value?  Is it perhaps the case that the "system oscillator" is in fact a buffer for an external crystal input and can be bypassed to enable use of an external digital clock signal?

Thanks

Martin

[lpcware]

Content originally posted in LPCWare by coatesm on Fri Oct 08 03:29:29 MST 2010
OK, that makes sense.  Thankyou for your help.

Martin

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Fri Oct 08 02:52:31 MST 2010
[FONT=Arial]User manual: [/FONT]

[LEFT][COLOR=#005042][COLOR=#005042][B][FONT=Arial][COLOR=#005042]3.4 Clocking and power control[/COLOR][/FONT][/B][/COLOR][/COLOR][/LEFT]

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Quote:

[FONT=Arial]The LPC111x/LPC11C1x include three independent oscillators. These are the system [/FONT][FONT=Arial]oscillator, the Internal RC oscillator (IRC), and the watchdog oscillator. Each oscillator can [/FONT][FONT=Arial]be used for more than one purpose as required in a particular application.[/FONT]

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[FONT=Arial]System oscillator is everything (your hardware!) you add to XTALIN / XTALOUT like crystal or oscillator circuit.[/FONT]

[lpcware]

Content originally posted in LPCWare by coatesm on Fri Oct 08 02:08:42 MST 2010
Hi,

Thankyou for your reply.  I understand how to change the clock speed and set up the PLL accordingly, I wanted to know if the system oscillator is an on-chip clock source, as the IRC oscillator is.  If that is the case I would have 3 options to clock the device:

1 - On chip IRC oscillator (12MHz)
2 - External Crystal (1-25MHz)
3 - On chip system oscillator (???)

Can you verify for me if this is the case please, and if so, what frequency the system oscillator is.

Thanks

Martin

[lpcware]

Content originally posted in LPCWare by CodeRedSupport on Thu Oct 07 07:08:24 MST 2010
If you just want to change the clock speed, the below FAQ may help to point you in the right direction....

http://support.code-red-tech.com/CodeRedWiki/LPC1xxxChangeClock

Regards,
CodeRedSupport