You start playfield display by making certain that the bitplane pointers are set and bitplane DMA is turned on. You turn on bitplane DMA by writing a 1 to bit BPLEN in the DMACON (for DMA control) register. See Chapter 7, System Control Hardware, for instructions on setting this register. Each time the playfield is redisplayed, you have to reset the bitplane pointers. Resetting is necessary because the pointers have been incremented to point to each successive word in memory and must be repointed to the first word for the next display. You write Copper instructions to handle the redisplay or perform this operation as part of a vertical blanking task.
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