Five possible positions can be chosen for each of the two "playfield fingers." For example,
you can place playfield 1 on top of sprites 0 and 1 (0), between sprites O and 1 and
sprites 2 and 3 (1), between sprites 2 and 3 and sprites 4 and 5 (2), between sprites 4
and 5 and sprites 6 and 7 (3), or beneath sprites 6 and 7 (4). You have the same
possibilities for playfield 2.
The numbers 0 through 4 shown in parentheses in the preceding paragraph are the actual
values you use to select the playfield priority positions. See "Setting the Priority Control
Register" below.
You can also control the priority of playfield 2 relative to playfield 1. This gives you
additional choices for the way you can design the screen priorities.
SETTING THE PRIORITY CONTROL REGISTER
This register lets you define how objects will pass in front of each other or hide behind
each other. Normally, playfield 1 appears in front of playfield 2. The PF2PRI bit reverses
this relationship, making playfield 2 more important. You control the video priorities by
using the bits in BPLCON2 (for "bit-plane control register number 2") as shown in Table 7-
1.
Table 7-1: Bits in BPLCON2
Bit
Number Name Function
15-7 Not used (keep at 0)
6 PF2PRI Playfield 2 priority
5-3 PF2P2 - PF2P0 Playfield 2 placement with
respect to the sprites
2-0 PF1P2 - PFlP0 Playfield 1 placement with
respect to the sprites
The binary values that you give to bits PF1P2-PF1P0 determine where playfield 1 occurs in
the priority chain as shown in Table 7-2. This matches the description given in the
previous section.
NOTE
PF2P2 - PF2P0, bits 5-3, are the priority bits for normal (non-dual) playfields.
- 204 System Control Hardware -
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