Interrupt Controller (8259A)
FUNCTIONAL DESCRIPTION
Figure 12-2 shows a block diagram of the 8259A. The PIC is divided
into eight major blocks for explanation purposes. Each of these
functional blocks is described in the following sections.
DATA
BUS
BUFFER
READ/
WRITE
CON-
TROL
LOGIC
CONTROL
WORD
REGISTER
INTERNAL BUS
RD
WR
AO
CS
INTERRUPT
REQUEST
REGISTER
(IRR)
CONTROL LOGIC
PRIORITY
RESOLVER
(PR)
INSERVICE
REGISTER
(ISR)
INTERRUPT MASK REGISTER
(IMR)
CAS 0
CAS 1
CAS 2
SP/EN
D7-D0
INTERNAL BUS
INTA
INT
Figure 12–2. 8259A Block Diagram.
12-7