CPU brake

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D2 brake for Amiga from Rex Datentechnik

The term CPU brakes were Cheat modules for home computers sold whose job it was the speed of the CPU to throttle. The purpose was to make computer games run slower so they would be easier to play.

However, since on many home computers ( C64 , Amiga ) the software was synchronized with the image display, i. H. the computation of a picture content had to be finished within one picture period (e.g. 50 Hz), the throttling of the CPU power led to the picture computation and display getting out of step, which led to strong jerking of the display. The player bought the simplification of the game with a significantly worse playability.

Technically, a CPU brake works as follows: A circuit generates a PWM signal with a fixed frequency. Via a potentiometer which is duty cycle set of the signal. The signal is then sent to the HALT pin of the CPU. When the HALT signal is active, the CPU is stopped. With 50% duty cycle, the CPU is only active half the time.