pub const MOS6530_DRA: u8 = 0x00;
pub const MOS6530_DDRA: u8 = 0x01;
pub const MOS6530_DRB: u8 = 0x02;
pub const MOS6530_DDRB: u8 = 0x03;

/*
0         X    Data Register A
1         X    Data Direction Register A
2         X    Data Register B
3         X    Data Direction Register B
4         0    Count down from value, divide by 1, disable IRQ 1    ???
5         0    Count down from value, divide by 8, disable IRQ 1    ???
6         0    Count down from value, divide by 64, disable IRQ 1    Read current counter value, disable IRQ
7         0    Count down from value, divide by 1024, disable IRQ 1    Read counter status, bit7 = 1 means counter past zero
8         X    Data Register A             (mirror ?)
9         X    Data Direction Register A   (mirror ?)
A         X    Data Register B             (mirror ?)
B         X    Data Direction Register B   (mirror ?)
C         0    Count down from value, divide by 1, enable IRQ 1    ???
D         0    Count down from value, divide by 8, enable IRQ 1    ???
E         0    Count down from value, divide by 64, enable IRQ 1    Read current counter value, enable IRQ
F         0    Count down from value, divide by 1024, enable IRQ 1    Read counter status, bit7 = 1 means counter past zero
*/