SPECIFYING THE DATA FETCH
The data-fetch registers specify the beginning and end positions for data placement on
each horizontal line of the display. You specify data fetch in the same way as shown in the
section called "Forming a Basic Playfield."
MEMORY ALLOCATION
For larger memory pictures, you need to allocate more memory. Here is a formula for
calculating memory requirements in general:
bytes per line * lines in playfield * # of bit-planes
Thus, if the wide playfield described in this section is formed from two bit-planes, it
requires:
80 * 200 * 2 = 32,000 bytes of memory
Recall that this is the memory requirement for the playfield alone. You need more memory
for any sprites, animation, audio, or application programs you are using.
SELECTING THE DISPLAY WINDOW STARTING POSITION
The display window starting position is the horizontal and vertical co-ordinates of the
upper left-hand corner of the display window. One register, DIWSTRT, holds both the
horizontal and vertical coordinates, known as HSTART and VSTART. The eight bits
allocated to HSTART are assigned to the first 256 positions, counting from the leftmost
possible position. Thus, you can start the display window at any pixel position within this
range.
- Playfield Hardware 71 -
To Next Page
Loading...
