Potentiometers
Eight ports to measurement increase of input. Each input has 8-bit timer, counting time when each TV line is being displayed. This had the added advantage of allowing the value read out to be fed directly into screen coordinates of objects being driven by the paddles. Each input has drop transistor, which can be set on or off from software. The timers can also be used to support a light pen, by connecting a photodiode to the drop transistor, which captures the timer when the electron beam in the television passes by the pen. The vertical position of the pen had to be read separately.
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