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
deutsch previous section next section

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