Commodore Amiga - Page 299

Read interrupt control register:
REG NAME
rn D6 OS D4 03 02 01 DO
o ICR
IR
o
o FLG SP ALRM TB TA
Write interrupt control MASK:
REG NAME rn D6 OS D4 03 02 01 DO
o
ICR
SIC x
x FLG SP ALRM TB TA
CONTROL REGISTERS
'!here are two control registers in the 8520, CRA and CRB. CRA is
associated with Timer A and CRB is associated with Timer B. The
format of the registers is as follows:
CONTROL REGISTER B:
BIT
NAME
o
1
2
3
4
START
PIlON
OU'OOOE
RUNMODE
LOAD
FUNCTION
1 = start Timer B, 0 = stop Timer B.
This bit is automatically reset (= 0) when
underflow occurs during one-shot mode.
1 =
Timer B output on PB7, 0 = PB7 is normal
operation.
1 = toggle, 0 = pulse.
1 = one-shot mode, 0 = continuous mode.
1 =
force load (this is a strobe input, there is no
data storage; bit 4 will always read back a
zero and writing a 0 has no effect.)
6,5 INK>OE Bits CRB6 and CRBS select one of four possible
input modes for Timer B, as follows:
CRB6 CRBS Mode Selected
CONTROL REGISTER A: ---------------------------------------
BIT NAME FUNCTION
o START 1 = start Timer A, 0 = stop Timer A.
This bit is automatically reset (= 0) when
underflow occurs during one-shot mode.
1
2
PBON 1 = Timer A output on PB6, 0 = PB6 is normal operation.
OU'OOOE 1 = toggle, 0 = pulse.
3 RUNMJOE 1 = one-shot mode, 0 = continuous mode.
4 LOAD
1 = force load (this is a strobe input, there is no
data storage; bit 4 will always read back a zero
and writing a 0 has no effect.)
5 INMODE 1 = Timer A counts positive CNT transitions,
o = Timer A counts 02 pulses.
6 SPK>DB 1 = Serial port=output (CNT is the source of the shift
clock)
o = Serial port=input (external shift clock is
required)
BIT MAP OF REGISTER CRA:
REG# NAME TOO IN SPK>DB INM:>DB LOAD RUNMJOB OU'D«>DE PBON
START
E CRA 0=60Hz O=input 0=02 l=force O=cont. O=pulse 0=PB6OFF O=stop
1=50Hz
l=output 1=CNT load l=one- l=toggle l=PB60N l=start
(strobe) shot
1<-------- Timer A Variables ----------------->1
All unused register bits are unaffected by a write and forced to 0 on a read.
7 ALARM
o
o
1
1
o
1
o
1
Timer B counts 02 pulses
Timer B counts positive CNT transitions
Timer B counts Timer A underflow pulses
Timer B counts Timer A underflow pulses
while CNT pin is held high.
1 = writing to TOO registers sets Alann
o = writing to TOO registers sets TOO clock.
Reading TOO registers always reads TOO clock,
regardless of the state of the Alann bit.
BIT MAP OF REGISTER CRB:
REG
:# NAME ALARM
INK>DE LOAD
RUNMODE OU'OOOE PIlON START
F CRB 0='1'00 00=02 l=force O=cont. O=pulse O=PB7OFF O=stop
l=Alann 01=CNT load l=one- l=toggle 1=PB7ON l=start
10=Timer A (strobe) shot
l1=CNT+
Timer A
I<----------------Timer B Variables--------------->I
All unused register bits are unaffected by a write and forced to 0 on
a read.
PORT SIGNAL ASSIGNMENTS
This part specifies how various signals relate to the available ports
of the 8520. This information enables the progralllllel" to relate the
port addresses to the outside-world items (or internal control signals)
which are to be affected. This part is primarily for the use of the