acme/ACME_Lib/cbm/cia.a

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;ACME 0.96.4
!ifdef lib_cbm_cia_a !eof
lib_cbm_cia_a = 1
; CBM's "complex interface adapter" chip, known as 6526.
; A newer version of this chip was initially called 8521, but later the name was
; changed back to 6526 again.
; There are two of these in a C64/128 computer, and one in 1570/1571 drives.
; pinout:
; ____ ____
; | V |
; GND | 1 40 | cnt clock for shift register
; / pa0 | 2 39 | sp data for shift register
; | pa1 | 3 38 | a0 \
; | pa2 | 4 37 | a1 |_ address
; Port _| pa3 | 5 36 | a2 | bus
; A | pa4 | 6 35 | a3 /
; | pa5 | 7 34 | /reset
; | pa6 | 8 33 | d0 \
; \ pa7 | 9 32 | d1 |
; / pb0 | 10 31 | d2 |
; | pb1 | 11 30 | d3 |_ data
; | pb2 | 12 29 | d4 | bus
; Port _| pb3 | 13 28 | d5 |
; B | pb4 | 14 27 | d6 |
; | pb5 | 15 26 | d7 /
; | pb6 | 16 25 | 0in clock
; \ pb7 | 17 24 | /flag
; /pc | 18 23 | /cs chip select
; tod_clk | 19 22 | r/w
; +5V | 20 21 | /irq
; |_________|
; register offsets:
; two 8-bit ports:
cia_port_a = $0
cia_port_b = $1
cia_data_direction_a = $2 ; clear means input,
cia_data_direction_b = $3 ; set means output
; two 16-bit timers, can be combined to form a single 32-bit timer:
cia_timer_a_low = $4
cia_timer_a_high = $5
cia_timer_b_low = $6
cia_timer_b_high = $7
; reading returns current counter value,
; writing sets start value.
; in 32-bit mode, timer A is "low word" and timer B is "high word".
; TOD (time of day) clock, clocked with 50 or 60 Hz:
; (CAUTION, registers use binary coded decimal format)
cia_timeofday_10ths = $8 ; %....3210 0..9, counts 10ths of seconds
cia_timeofday_seconds = $9 ; %.6543210 0..59, as two BCD digits:
; %.654.... 0..5 "tens"
; %....3210 0..9 "ones"
cia_timeofday_minutes = $a ; %.6543210 0..59, as two BCD digits:
; %.654.... 0..5 "tens"
; %....3210 0..9 "ones"
cia_timeofday_hours = $b ; %7..43210 AM/PM and 1..12 as two BCD digits:
; %7....... 0 means AM, 1 means PM
; %...4.... 0..1 "tens"
; %....3210 0..9 "ones"
; when reading or writing time, start with hours and end with 10ths:
; accessing hours uncouples registers from clock, accessing 10ths re-couples them.
; if your read access does not start with the hours register,
; you have a race condition!
; shift register:
; msb is sent/received first. send clock is half of timer A's underflow rate.
cia_serial_data = $c
; control registers:
cia_interrupt_control = $d
; %7....... read: 1 = interrupt requested
; write: 0 = disable interrupts indicated by set bits
; 1 = enable interrupts indicated by set bits
; %.65..... unused
; %...4.... negative edge on /flag detected
; %....3... shift register has finished sending or receiving
; %.....2.. time of day alarm
; %......1. timer B underflow
; %.......0 timer A underflow
cia_control_a = $e
; %7....... TOD clock: 0 means 60 Hz, 1 means 50 Hz
; %.6...... shift register direction: 0 = input, 1 = output
; %..5..... timer A clock: 0 = system clock, 1 = CNT
; %...4.... 1 = force load timer start value
; %....3... timer mode: 0 = continuous, 1 = one-shot (needs restart via bit 0)
; %.....2.. 0 = pulse on PB6, 1 = invert PB6
; %......1. 1 = timer underflow shows on PB6 (this forces PB6 to output)
; %.......0 0 stops timer, 1 starts timer
cia_control_b = $f
; %7....... TOD write mode: 0 = actual time, 1 = alarm time (it is not possible to _read_ the alarm time!)
; %.65..... timer B clock:
; %00 = system clock
; %01 = CNT
; %10 = underflow of timer A
; %11 = combination of %01 and %10
; %...4.... 1 = force load timer start value
; %....3... timer mode: 0 = continuous, 1 = one-shot (needs restart via bit 0)
; %.....2.. 0 = pulse on PB7, 1 = invert PB7
; %......1. 1 = timer underflow shows on PB7 (this forces PB7 to output)
; %.......0 0 stops timer, 1 starts timer