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M1284p at 25Mhz

 
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Paulvk

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Joined: 28 Jul 2006
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Location: SYDNEY

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PostPosted: Wed Jul 18, 2012 10:25 am    Post subject: M1284p at 25Mhz Reply with quote

Has anyone tried to run a M1284p at 25Mhz the reason I ask is that after 12.5Mhz theENC28J60 puts out 25Mhz. I am waiting on some more M1284p chips to arrive (only have one) before I try the setting.

Regards Paul
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hgrueneis

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Joined: 04 Apr 2009
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Location: A-4786 Brunnenthal

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PostPosted: Thu Jul 19, 2012 1:20 am    Post subject: Reply with quote

Paul,
have used it with an external clock at 24 MHz (Oscillator, not a crystal) on the 1284p and the 168 with success and without failure.
On one of the old 168 datasheets, the max. clock for 5V is even specified with 24 MHz!
With plain crystals (can and smd) I have had too many failures of not starting at standard frequencies.
Crystals are off limit for me now. Either internal OSC or external clock.
At some point with higher clocks, the input sometimes only took every other cycle (half the frequency).
I'm certain it will not work at a lower supply.
Try it, it either works or not. The chips (up to now) did not take any damage.
Hubert
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Paulvk

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PostPosted: Thu Jul 19, 2012 1:52 am    Post subject: Reply with quote

Hi Hubert

Found this interesting article linux 32bit running at 24Mhz http://dmitry.co/index.php?p=./04.Thoughts/07.%20Linux%20on%208bit#uniqstr_1342658930940_q be nice to have the code for sdram in bascom.

Regards Paul
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hgrueneis

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Joined: 04 Apr 2009
Posts: 863
Location: A-4786 Brunnenthal

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PostPosted: Thu Jul 19, 2012 4:20 am    Post subject: Reply with quote

Hi Paul,
Thanks for the great link.
Some things never change much...reminds me of the way CPM used to boot and load on the 8080 (Z80) systems.
Fiddled on that a lot with changes.
It was "slightly" faster, especially with 6.144 MHz.
It certainly has potential, just can't think of any useful application just now.
It kind of limits it when the wait for a boot is a day.
Have to drink a lot of coffee!
Thanks again.
Hubert
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