Commodore Amiga A500 Technical Reference Manual page 119

HOW to Clear an
Asserted Interrupt
Signal
AMIGA SIDE
Amiga Interrupt Status
Register (R)
(1FFF1 / 17FFF1)
PC Interrupt Status
Register (R)
(1FFF3 / 7FFF3)
INT
|RQ3_a
IRQ3_b
IRQ7
All registers on the memory locations 1FFFO TO 1FFFF are only
accessable from the AMIGA side.
Reading this register returns the interrupt events caused on PC ac-
cesses as follows:
Bit no. Function
0 Mono Video Ram
1 Color Video Ram
2 Mono CRT
3 Color CRT
4 Keyboard Register
5 LPT1 Control Reg
6 COM2 Data Reg
7 see PC System Status Res ( /SYSINT
The event was valid if the bit is set to " 1". After reading the register all
bits turns to "0" automatically and the interrupt flag will be
negated.
Reading this register returns the pending PC interrupts on the lower
nibble. The PC interrupt is asserted as shown by the corresponding
bit in the table.
Bit no. Function
0 IRQ1 (Keyboard interrupt)
1 IRQ3_a
2 IRQ3_b
3 IRQ7
4-7 NOT USED, always HIGH
Bit 1 and bit 2 (IRQ3_a and lRQ3_b) are externally "ORed" to 1RQ3
116
Negation
Read to i/o location 3bO hex
Read com2 register 2F8 hex
Read line printer status register 379 hex
( /MINT )
( /GINT )
( /CRT1INT )
( /CRT2INT )
( /ENBKB )
( /LPT1INT )
( /C0M2INT )
)
Asserted if
1
0
0
0