The MOS 6567/6569 video controller (VIC-II) and its application in the Commodore 64
Contents 3. Description of the VIC
3.13. DRAM refresh |
The VIC does five read accesses in every raster line for the refresh of the dynamic RAM. An 8 bit refresh counter (REF) is used to generate 256 DRAM row addresses. The counter is reset to $ff in raster line 0 and decremented by 1 after each refresh access. So the VIC will access addresses $3fff, $3ffe, $3ffd, $3ffc and $3ffb in line 0, addresses $3ffa, $3ff9, $3ff8, $3ff7 and $3ff6 in line 1 etc.
Refresh adresses
13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0
1 | 1 | 1 | 1 | 1 | 1 | REF7 | REF6 | REF5 | REF4 | REF3 | REF2 | REF1 | REF0