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The CIA 6526 is an I/O port chip with 2 8-bit I/O ports, a shift register, two timers, a Time of Day clock and interrupts.
Version numbers: Major 1, Minor 1.
Type | Name | Description |
BYTE | ORA | Output register A |
BYTE | ORB | Output register B |
BYTE | DDRA | Data direction register A |
BYTE | DDRB | Data direction register B |
WORD | TAC | Timer A counter value |
WORD | TBC | Timer B counter value |
BYTE | TOD_TEN | Time of Day - current tenth of second |
BYTE | TOD_SEC | Time of Day - current seconds |
BYTE | TOD_MIN | Time of Day - current minutes |
BYTE | TOD_HR | Time of Day - current hours |
BYTE | SDR | contents of shift register |
BYTE | IER | mask of enabled interrupt masks |
BYTE | CRA | Control register A |
BYTE | CRB | Control register B |
WORD | TAL | Timer A latch value |
WORD | TBL | Timer B latch value |
BYTE | IFR | mask of currently active interrupts |
BYTE | PBSTATE | Bit 6/7 reflect the PB6/7 toggle bit state. Bit 2/3 reflect the corresponding port bit state. |
BYTE | SRHBITS | number of half-bits to still shift in/out SDR |
BYTE | ALARM_TEN | Time of Day - alarm tenth of second |
BYTE | ALARM_SEC | Time of Day - alarm seconds |
BYTE | ALARM_MIN | Time of Day - alarm minutes |
BYTE | ALARM_HR | Time of Day - alarm hours |
BYTE | READICR | current clock minus the clock when ICR was read last plus 128. |
BYTE | TODLATCHED | Bit 0: 1= latched for reading, Bit 1: 2=stopped for writing |
BYTE | TODL_TEN | Time of Day - latched tenth of second |
BYTE | TODL_SEC | Time of Day - latched seconds |
BYTE | TODL_MIN | Time of Day - latched minutes |
BYTE | TODL_HR | Time of Day - latched hours |
DWORD | TOD_TICKS | clk ticks till next tenth of second |
– | – | The next items have been added in V1.1 |
WORD | TASTATE | The state bits of the CIA timer A, according to ciatimer.h |
WORD | TBSTATE | The state bits of the CIA timer B, according to ciatimer.h |
The last two items have been added in CIA snapshot version 1.1 due
to the improved CIA emulation in the newer VICE versions.
Some state bits correspond to the CIA state as described in the
"A Software Model of the CIA 6526" document by Wolfgang Lorenz,
some are delayed versions. For more read the source file
ciatimer.h
.
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