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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Powerup RAM test pattern
What are those patterns of sixty four trailing 0x00 and 0xff in RAM. Are those powerup test patterns to check wether the bits are working?
Reason I am asking is that I have just ignored figuring out what causes it in the past. Im not usually diging deep into the electronics. Also I am looking at some older computer than C64 which has the same pattern; though those are 128 bytes long instead of 64 but has the same amount of RAM. So whats the reason C64 has 64 bytes of these and not 128?
Two quick questions. Feel free to enlighten me :P |
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Krill
Registered: Apr 2002
Posts: 2825 |
Short answer is, it's the "natural" state the memory bits fall back to after not being refreshed for a certain time. A hardware effect.
Why this is 0 for some ranges and 1 for others, and the size of those ranges, is part of the long answer. |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Very good |
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Impetigo
Registered: Jun 2004
Posts: 30 |
A relevant discussion: what is your RAM init pattern? |
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chatGPZ
Registered: Dec 2001
Posts: 11100 |
also see https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/C64.. |
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Rudi
Account closed
Registered: May 2010
Posts: 125 |
Thank you |
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Oswald
Registered: Apr 2002
Posts: 5017 |
Quote: Short answer is, it's the "natural" state the memory bits fall back to after not being refreshed for a certain time. A hardware effect.
Why this is 0 for some ranges and 1 for others, and the size of those ranges, is part of the long answer.
that makes me remember, in the "days" we had no carts we just power cycled to reset the machines, at one of my friends once the c64 just didnt want to forget, the screen was still there after 3-5 power cycles altho more and more degraded, the program obviously not running. Then after waiting some minutes it was fine. |
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chatGPZ
Registered: Dec 2001
Posts: 11100 |
yes, a certain type of (iirc) chinese RAMs had a crazy long retention time - long enough for some games with cbm80 startup to just start again after quick powercycle :) |
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Repose
Registered: Oct 2010
Posts: 222 |
That happened to my machine too. I wonder if they are still powered at least by some capacitor, but I don't recall experimenting with unplugging it.
However, it's never a bug it's a feature - I wanted to write a simple error correcting code, using a large amount of memory to store a time string, so I could log brief power outs! |
