System Interrupts; Interrupt Controller - HP Vectra Reference Manual

System Interrupts
The 80286 microprocessor provides a non-maskable interrupt
(NMI) bit that can be set and reset with system programs. An
interrupt controller provides another 19-1evels of system interrupt.
The Intel 8259A interrupt controller chip U107 is the master chip.
Cascaded to the master chip are two other 8259A chips. Each
chip has an 8-bit interrupt request function. The primary function
of the third controller chip is keyboard and input device interface.
The following chart gives the port addresses of the interrupt
controllers.
020H Master 8259A Port 0
021H Master 8259A Port 1
OAOH
Slave 8259A (#2) Port 0
OA1H Slave 8259A (#2) Port 1
07CH Slave 8259A (#3) Port 0
07DH
Slave 8259A (#3) Port 1
Interrupt Controller
The following figure indicates the possible interrupt vector offset
mappings. The current address in hex is given in the parentheses.
In the far right hand column is the function of the interrupt vector
employed by HP Vectra.
20 Processor Board