In the past game controllers were just buttons. For example, the NES controller (on the right) had 8 buttons. This made it very easy for the computer to read what buttons were pressed. The NES uses a modified version of the 6502 as the brains of the console. The computer I am building also uses the same chip. I want to make games similar to those on the NES so it would be logical to follow the design of the NES. I could make an 8 button digital controller but that is boring. More modern controllers use analogue joysticks. It would be more advanced to build a modern controller and allow for more advanced applications. I decided I would use a premade analogue to digital converter because I prefer working in digital applications. The chip used a serial interface meaning each bit was sent to the computer in order instead of all of the bits at once. I was able to design a simple program to interface with the chip. I was able to successfully get an digital signal back but it was slow. I decided I would make a circuit that would convert the analogue signal into a parallel 8 bit value which my computer could read back. This would speed up the process of getting joystick values back because now I just had to a read a value. The circuit communicates with the chip and then shifts the values out into a shift register. This shift register is then outputted back to the computer at address 1. In the video above you can see me move the joystick left and right and in the background a set of 8 blue LEDs outputs the joystick position as an 8 bit value.
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