Re: [uCsimm] LCDs and 20Mhz clock rate

From: David Williams (
Date: Thu Jun 22 2000 - 20:20:25 EDT

As far as the clock rate is concerned changing the rate is simply a matter of
reprogramming the PLL registers so that the PLL generates 20MHz (derived from the
32KHz). However you must ensure that the 68EZ328 part you are using is a 20MHz part
otherwise you are running the device out of spec (overclocking - which may or may not
work). After this you must then consider that various internal clocks/timers may be
affected if SYSCLK (the main CPU speed) is changed. Changing the SYSCLK may or may
not require you to change to prescaler. If so then the LCDCLK and DMACLK are also
affected. If not then only SYSCLK is affected. If SYSCLK is being used to drive the
internal timer then the timer frequency will also change. SYSCLK is typically used
for baud rate generation as well for the UART. Thus baud rate generation will also
change. As for uClinux I suspect that some changes would be required somewhere if you
change the SYSCLK. I dont use it, but I am sure others can help with this.


Marc Nicholas wrote:

> Hi there...
> Can someone suggest a relatively cheap, easy to interface LCD that'll work
> with the uCsimm?
> Also, is it easy to up the clock rate from 16Mhz to 20Mhz?
> Thanks.
> -marc
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