Re: mega128 at 18.432 MHz

At 10:30 06/01/2004 -0800, Theodore A. Roth wrote:
>Hi,
>
>Has anyone tried running a mega128 using a 18.4320 MHz crystal?
>
>I found some websites where some dish network hackers are using >16Mhz
>crystals on an access card running a mega128.
>
>If the mcu can handle the higher clock rate, it seems like a cheap way
>to get a 20% performance boost over using a 14.7456 MHz crystal while
>still having accurate (0% error) serial port access.

The usual method used to determine successful operation at higher 
frequencies is to keep going until it starts to show failure whilst running 
a series of tests that exercise the RAM, EEPROM,  and periperials etc.  Try 
to obtain a range of devices with varying manufacture dates and repeat 
tests at different temperatures also.  If they all started failing at 
around 24.5MHZ then 22.1184MHz is too close and 18.432MHz is going to be fine.

 From memory I think the EEPROM craps out first.

Perhaps a few people would be willing to try overclocking m128's and we can 
collate the results?  If a common test program was written this would 
almost be scientific <grin>

Would be quite useful to know if 18.432MHz is safely achievable.  Of note 
is the datasheet USART baud rate table showing clock frequencies upto 20MHz.


Jason Kyle

>Ted Roth