| Vss | 1 | -6520 PIA- -6821 PIA- |
40 | ca1 | <-- | |
| <-> | pa0 | 2 | 39 | ca2 | <-- | |
| <-> | pa1 | 3 | 38 | !irqa | --> | |
| <-> | pa2 | 4 | 37 | !irqb | --> | |
| <-> | pa3 | 5 | 36 | a1 | <-> | |
| <-> | pa4 | 6 | 35 | a0 | <-> | |
| <-> | pa5 | 7 | 34 | !rst | <-- | |
| <-> | pa6 | 8 | 33 | d0 | <-> | |
| <-> | pa7 | 9 | 32 | d1 | <-> | |
| <-> | pb0 | 10 | 31 | d2 | <-> | |
| <-> | pb1 | 11 | 30 | d3 | <-> | |
| <-> | pb2 | 12 | 29 | d4 | <-> | |
| <-> | pb3 | 13 | 28 | d5 | <-> | |
| <-> | pb4 | 14 | 27 | d6 | <-> | |
| <-> | pb5 | 15 | 26 | d7 | <-> | |
| <-> | pb6 | 16 | 25 | ph2 | <-- | |
| <-> | pb7 | 17 | 24 | cs1 | <-- | |
| <-> | cb1 | 18 | 23 | !cs2 | <-- | |
| <-> | cb2 | 19 | 22 | cs0 | <-- | |
| Vcc | 20 | 21 | r/!w | <-- |
PIA controls various I/O.
In the Atari 800XL: base address = $D300
struct PIA = // a standard 6520 chip
{
byte PORTA; // Port A
byte PORTB; // Port B
byte PACTL; // Port A Control
byte PBCTL; // Port B Control
};
Approximate VHDL entity only!
entity PIA_6520 is -- a standard 6520 chip port( n_rst: in std_logic; -- Reset n_wr: in std_logic; -- Read / Not Write ph2: in std_logic; -- CPU clock phase 2 cs0: in std_logic; cs1: in std_logic; n_cs2: in std_logic; a: in std_logic_vector(1 downto 0); d: inout std_logic_vector(7 downto 0); pa: inout std_logic_vector(7 downto 0); -- Port A ca: inout std_logic_vector(2 downto 1); -- Port CA pb: inout std_logic_vector(7 downto 0); -- Port B cb: inout std_logic_vector(2 downto 1); -- Port CB n_irqa: out std_logic; -- interrupt request A n_irqb: out std_logic; -- interrupt request B ); end entity PIA_6520;