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.


The PIA functions are best examined in the following sections, which show how to use them.

TimersInterval Timers
RAMInternal system RAM
IO PortsSystem IO


For details on individual registers, click on the register name in the following table.

$280SWCHAPort A; input or output (read or write)
Used for controllers (joystick, paddles, etc.)
$281SWACNTPort A data direction register, 0= input, 1=output
$282SWCHBPort B; console switches (read only)
$283SWBCNTPort B data direction register (hardwired as input)
$284INTIMTimer output (read only)
$285INSTATTimer status (read only)
$294TIM1Tset 1 clock interval (838 nanosecond/interval)
$295TIM8Tset 8 clock interval (6.7 microsecond/interval)
$296TIM64Tset 64 clock interval (53.6 microsecond/interval)
$297T1024Tset 1024 clock interval (858.2 microsecond/interval)


  • one clock is also one microprocessor machine cycle