The TIA (as seen by the programmer)

5.0 Playfield

The PF register is used to create a playfield of walls, clouds, barriers, etc., that are seldom moved. This low resolution register is written into to draw the left half of the TV screen only. The right half of the screen is drawn by software selection of whether a duplication or a reflection of the right half.

The PF register is 20 bits wide, so the 20 bits are written into 3 addresses: PF0, PF1, and PF2. PF0 is only 4 bits wide and constructs the first 4 bits of the playfield, starting at the left edge of the TV screen. PF1 constructs the next 8 bits, and PF2 the last 8 bits which end at the center of the screen. The PF register is scanned from left to right and where a 1 is found the PF color is drawn, and where a 0 is found, the BK color is drawn. To clear the playfield, obviously zeros must be written into PF0, PF1, and PF2.

To make the right half of the playfield into a duplication or copy of the left half, a 0 is written to D0 of the CTLPF (control playfield) register. Writing a 1 will cause the reflection to be displayed.

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See also: 'TIA 1A - TELEVISION INTERFACE ADAPTOR (MODEL 1A) - 3. Playfield graphics Register'