Either playfield 1 or 2 may have priority; that is, either one may be displayed in front of the other. Playfield 1 normally has priority. The bit known as PF2PRI (bit 6) in register BPLCON2 is used to control priority. When PF2PRI = 1, playfield 2 has priority over playfield 1. When PF2PRI = 0, playfield 1 has priority. You can also control the relative priority of playfields and sprites . Chapter 7, System Control Hardware, shows you how to control the priority of these objects. You can control the two playfields separately as follows: * They can have different-sized representations in memory, and different portions of each one can be selected for display. * They can be scrolled separately. An important warning. --------------------- You must take special care when scrolling one playfield and holding the other stationary. When you are scrolling low resolution playfields, you must fetch one word more than the width of the playfield you are trying to scroll (two words more in high resolution mode) in order to provide some data to display when the actual scrolling takes place. Only one data-fetch start register and one data-fetch stop register are available, and these are shared by both playfields. If you want to scroll one playfield and hold the other, you must adjust the data-fetch start and data-fetch stop to handle the playfield being scrolled. Then, you must adjust the modulo and the bitplane pointers of the playfield that is not being scrolled to maintain its position on the display. In low resolution mode, you adjust the pointers by -2 and the modulo by -2. In high resolution mode, you adjust the pointers by -4 and the modulo by -4.
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