Peripheral Interface Adaptor
The PIA chip is an off-the-shelf 6532 Peripheral Interface Adaptor which has three functions: a programmable timer, 128 bytes of RAM, and two 8 bit parallel I/O ports.
Grouped
The PIA functions are best examined in the following sections, which show how to use them.
| Timers | Interval Timers | |
| RAM | Internal system RAM | |
| IO Ports | System IO | |
Registers
For details on individual registers, click on the register name in the following table.
| Name | Purpose | |
| $280 | SWCHA | Port A; input or output (read or write) Used for controllers (joystick, paddles, etc.) |
| $281 | SWACNT | Port A data direction register, 0= input, 1=output |
| $282 | SWCHB | Port B; console switches (read only) |
| $283 | SWBCNT | Port B data direction register (hardwired as input) |
| $284 | INTIM | Timer output (read only) |
| $285 | INSTAT | Timer status (read only) |
| $294 | TIM1T | set 1 clock interval (838 nanosecond/interval) |
| $295 | TIM8T | set 8 clock interval (6.7 microsecond/interval) |
| $296 | TIM64T | set 64 clock interval (53.6 microsecond/interval) |
| $297 | T1024T | set 1024 clock interval (858.2 microsecond/interval) |
Notes
- one clock is also one microprocessor machine cycle