Interrupt Controller (8259A)
OVERVIEW
The Programmable Interrupt Controller (PIC) is an Intel 8259A
device (or equivalent). It is capable of monitoring eight interrupt
inputs with programmable priority. When peripherals request service,
the PIC interrupts the CPU with a pointer to a service routine for the
highest priority device.
This pointer is often called a "vector."
Interrupt management of this type is needed for an efficient interface
between the CPU and supporting peripheral devices, such as serial
controllers and counter/timers. The major features of the PIC are as
follows:
•
Eight individually maskable interrupts
•
Extended operation for additional interrupts
•
Level- or edge-triggered interrupts
•
Fixed and rotating prioritization
•
Status for polled operation
•
Equivalent to the PIC used in IBM PCs and compatibles
•
I/O addresses equivalent to IBM PCs and compatibles
I/O PORT ADDRESSES
I/O port addresses used by the 8259A are 0020h - 0021h. Use of these
addresses is described beginning on page 12-21. The PIC actually
occupies addresses 0020h - 0027h, mapping it redundantly every two
I/O addresses in this range.
12-3
Содержание ZT 8809A
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