Classic Computer Magazine Archive COMPUTE! ISSUE 50 / JULY 1984 / PAGE 6

Reading The Atari 800 PIA Registers

I am 16 years old and own an Atari 800. Currently, I am trying to use the joystick ports for certain I/O applications. So far, the only problem I've encountered is speed. The registers that store input information from the joyports are updated only every sixtieth of a second. This is too slow for me. Is there any way to read the joystick ports at a faster rate?

Christopher Terpin

Instead of using the shadow locations for the joysticks, you can read the joystick ports directly from the data direction registers in the 6520 PIA chip. These are truly general-purpose input/output ports, with one byte used for two joysticks. Each bit can be programmed independently for input and output. Complete information on this can be found in the Atari Hardware Reference Manual. Some information is also found in Mapping the Atari, available from COMPUTE! Books. In the meantime, examine the information found at $D300.