7. Collision Detection Latches

A. Definitions

The serial outputs from all the graphics registers represent real time horizontal location of objects on the television screen. If any of these outputs occur at the same time, they will overlap (collide) on the screen. There are six objects generated on this chip (five moving and playfield) allowing fifteen possible two object collisions. These overlaps (collisions) are detected by fifteen "and" gates whenever they occur, and are stored in fifteen individual latch register bits, as shown in figure 6.

B. Reading Collision

The microprocessor can read these fifteen collision bits on data lines 6 and 7 by addressing them two at a time. This could be done at any time but is usually done between frames (during vertical blank) after all possible collisions have serially occurred.

C. Reset

All collision bits are reset simultaneously by the microprocessor using the reset address CXCLR. This is usually done near the end of vertical blank, after collisions have been tested.

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