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The VIA 6522 is the predecessor of the CIA and also an I/O port chip with 2 8-bit I/O ports, a shift register, two timers and interrupts.
Version numbers: Major 1, Minor 0.
Type | Name | Description |
BYTE | ORA | Output register A |
BYTE | DDRA | Data direction register A |
BYTE | ORB | Output register B |
BYTE | DDRB | Data direction register B |
WORD | T1L | Timer 1 Latch value |
WORD | T1C | Timer 1 counter value |
BYTE | T2L | Timer 2 latch (8 bit as only lower byte is used) |
WORD | T2C | Timer 2 counter value |
BYTE | RUNFL | bit 7: timer 1 will generate IRQ on underflow; bit 6: timer 2 will generate IRQ on underflow |
BYTE | SR | Shift register value |
BYTE | ACR | Auxiliary control register |
BYTE | PCR | Peripheral control register |
BYTE | IFR | active interrupts |
BYTE | IER | interrupt mask |
BYTE | PB7 | bit 7 = pb7 state |
BYTE | SRHBITS | number of half-bits to shift out on SR |
BYTE | CABSTATE | bit 7: state of CA2 pin, bit 6: state of CB2 pin |
BYTE | ILA | Port A Input Latch (see ACR bit 0) |
BYTE | ILB | Port B Input Latch (see ACR bit 1) |