Tandy 1000 HX Technical Reference Manual page 123

8259A
PROGRAMMABLE INTERRUPT CONTROLLER
8259A/8259A-2/8259A-8
8086, 8088 Compatible
MCS-80®, MCS-85® Compatible
Eight-Level Priority Controller
Expandable to 64 Levels
Programmable Interrupt Modes
Individual Request Mask Capability
Single +5V Supply (No Clocks)
28-Pin Dual-ln-Line Package
Available in EXPRESS
— Standard Temperature Range
— Extended Temperature Range
The Intel 8259A Programmable Interrupt Controller handles up to eight vectored priority interrupts for the CPU.
It is cascadable for up to 64 vectored priority interrupts without additional circuitry. It is packaged in a 28-pin
DIP, uses NMOS technology and requires a single + 5V supply. Circuitry is static, requiring no clock input.
The 8259A is designed to minimize the software and real time overhead in handling multi-level priority inter-
rupts. It has several modes, permitting optimization for a variety of system requirements.
The 8259A is fully upward compatible with the Intel 8259. Software originally written for the 8259 will operate
the 8259A in all 8259 equivalent modes (MCS-80/85, Non-Buffered, Edge Triggered).
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Order Number 231468-001
Figure 1. Block Diagram