Lpc2000

Hello,

has someone used the LPC2106 with a oscillator frequency of 2,5 MHz or 5
MHz?
According to data sheet it should be between 10 and 25 MHz.
It needn't to be fully stable (a few minutes to hour is enough), because it
is only for a short measurement task. Internally i still want to use the PLL
with M = 11 and P = 4 to get a internal frequency of 27,5 MHz or 55 MHz.

Is the PLL still running at such low frequencies ? Are there any known side
effect, that core or peripheral is not working anymore ?

Regards,

         Martin

--- In lpc2000@yahoogroups.com, capiman@t... wrote:
> Hello,
> 
> has someone used the LPC2106 with a oscillator frequency of 2,5 MHz or 5
> MHz?
> According to data sheet it should be between 10 and 25 MHz.
> It needn't to be fully stable (a few minutes to hour is enough),
because it
> is only for a short measurement task. Internally i still want to use
the PLL
> with M = 11 and P = 4 to get a internal frequency of 27,5 MHz or 55 MHz.
> 
> Is the PLL still running at such low frequencies ? Are there any
known side
> effect, that core or peripheral is not working anymore ?

I don't know specifically about this part, but most PLLs are built
with a filter.  That is what limits the frequency range.  If the input
frequency to the phase detector is too low, the filter will not do a
good job of filtering the control voltage to the VCO and the frequency
will vary (jitter).  

My guess is that if you work with 5 MHz input, you will find it to
work ok.  But isn't the feedback divider limited to 6?  I don't think
you will be able to output higher than 30 MHz.  Or are there larger
values that you are simply warned not to use?