Specifications

Chapter 12
INTERRUPT CONTROLLER (8259A)
Contents Page
OVERVIEW .................................................... 12-3
I/O PORT ADDRESSES
......................................... 12-3
OPERATION OVERVIEW
....................................... 12-4
FUNCTIONAL DESCRIPTION
.................................. 12-7
Interrupt Request Register (IRR)
.............................. 12-8
Interrupt Mask Register (IMR)
................................ 12-8
Priority Resolver (PR)
....................................... 12-9
Interrupt In-Service Register (ISR)
............................ 12-9
Control Logic
............................................... 12-9
Read/Write Control Logic
................................... 12-10
Initialization and Operation Registers
......................... 12-10
Cascade Buffer/Comparator
................................. 12-10
PROGRAMMABLE REGISTERS
............................... 12-11
Initialization Control Words (ICW1-4)
........................ 12-12
ICW1
................................................. 12-12
ICW2
................................................. 12-14
ICW3
................................................. 12-14
ICW4
................................................. 12-15
ICW Summary
......................................... 12-16
Operation Control Words (OCW1-3)
......................... 12-16
OCW1
................................................ 12-18
OCW2
................................................ 12-18
OCW3
................................................ 12-19
8259A I/O PORT ADDRESSES
................................. 12-21
INTERRUPT ASSIGNMENTS ON THE ZT 8809A
............... 12-22
OPERATION OF THE INTERRUPT CONTROLLER
............. 12-24
Priorities
.................................................. 12-24
Fully Nested Mode
..................................... 12-24
12-1