Hi Ruud, On Wed, Oct 12, 2016 at 05:15:44AM +0000, Baltissen, GJPAA (Ruud) wrote: >Hallo Gerrit, > > >> 41256 need 8Bit refresh... > >Nope. Otherwise the Finnish's and the 64'er's 256 KB hack on the C64 wouldn't >have worked. The VIC-II in the C64 (as well as the VIC-IIe in the C128) implements an 8-bit refresh counter. That was proven in 1994 by the test program that Andreas Boose wrote, to check which memory addresses the VIC-II chip is reading. (On each line, for 5 clock cycles it would read from the $3f00..$3fff area. I cannot remember if the 8-bit counter was increasing or decreasing, for those 5 cycles per line.) If there only is a 7-bit refresh counter available on the PET, Gerrit made a very valid point. Half of the DRAM could get corrupted, except if the program is accessing the 'missing' addresses frequently enough. But, unless I am mistaken, you would still get reliable 128 kilobits out of each 41256 chip. Didier made a good point too. I would not want to have flying wires nowadays either. Back then I was young and brave (or stupid). :) Marko Message was sent through the cbm-hackers mailing listReceived on 2016-10-12 06:00:02
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