The steps for defining a scrolled playfield are the same as those for defining the basic playfield, except for the following steps: * Defining the data fetch . ------------------------- Fetch one extra word per horizontal line and start it 16 pixels before the normal (unscrolled) data-fetch start. * Defining the modulo . --------------------- The modulo is two counts less than when there is no scrolling. These steps are added: * For vertical scrolling , reset the bitplane pointers ----------------------------------------------------- for the amount of the scrolling increment. ----------------------------------------- Reset BPLxPTH and BPLxPTL during the vertical blanking interval. * For horizontal scrolling , specify the delay. --------------------------------------------- Set bits 7-0 in BPLCON1 for 0 to 15 bits of delay.
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