Atari 400 Technical Reference Manual page 87

6 INTERRUPT PROCESSING
Section 6 describes system actions for the various interrupt
causing events, defines the many RAM vectors and provides
recommended procedures for dealing with interrupts.
The
6502
microcomputer processes three general interrupt types:
chip-reset, nonmaskable interrupts (NMI) and maskable interrupts
(IRQ). The IRQ interrupt type can be enabled and disabled using
the
6502
eLI and SEI instructions. The NMI type cannot be
disabled at the processor leveli but the NMI interrupts other
than [SYSTEM. RESET] key can be disabled at the ANTIC chip.
The system events that can cause interrupts are listed below:
chip-reset - power-up
NMI - Display list interrupt <unused by aS)
vertical-blank
(50/60
Hz)
(SYSTEM. RESET] key
IRQ - Serial bus output ready
Serial bus output complete
Serial bus input ready
Serial bus proceed line <unused by system)
Serial bus interrupt line <unused by system)
POKEY timers 1, 2 and 4
Keyboard key
[BREAK] key
6502
BRK instruction <unused by OS)
Figure 6-1 List of System-Interrupt Events
OPERATING SYSTEM C016555 -- Section 6
102