Posted By
Gaia
on 2007-04-15
12:34:58
|  Re: FLD on +4?
Oops, the DMA story could fill a whole book  As a rule of thumb: do not rely too much on your knowledge of the C64 as although the basic mechanism is very similar, there are subtle differences between the two machines. For a few ideas of FLD on the plus/4, you can check a couple of demos that were basically converted from C64 (like A Trip for example).
FLD is also depending on whether you are using text or bitmap mode. FF1A/B does not play a role in text mode (unless you're messing with the cursor). If you delay the first "bad line" (aka DMA line) by appropriately changing the lowest 3 bits of FF06 not to be equal to that of FF1C/D, you are basically doing an FLD. You can do the same in bitmap mode by not allowing the lowest 3 bits of FF1F to be 7 (the vertical sub address, increasing every non idle TED rasterline).
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