On Thu, Oct 13, 2016 at 08:45:12AM +0300, Marko Mäkelä wrote: > On Wed, Oct 12, 2016 at 10:49:09PM +0100, smf wrote: > >The apple 2 apparently doesn't have dram refresh, it uses the video > >fetches to refresh the memory. I'm not sure why the c64 is different. > > I think that the memory refresh access cycles (5 per scan line) come > into rescue when the video output is blanked, no sprites are enabled, > and the CPU is executing in a tight loop, covering only a few addresses > for a longer period of time. In this configuration, the VIC-II would be > accessing $3fff all the time, except for the 5 refresh cycles per scan > line. This is also what happens when the vertical border or the vertical > blanking is being generated. The original VIC-II (the 6566) used SRAM. To make the DRAM versions it probably was a lot easier to add this simple counter than to change all timing stuff to make sure all rows were accessed often enough (also during "border time", etc. -- the DRAMs need to be refreshed a whole bunch of times per frame). Segher Message was sent through the cbm-hackers mailing listReceived on 2016-10-13 07:00:02
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