8259A Datasheet, PDF (11/24 Pages) Intel Corporation – PROGRAMMABLE INTERRUPT CONTROLLER

8259A
Initialization Command Word 4 (ICW4)
SFNM If SFNM ^e 1 the special fully nested mode
is programmed
BUF
If BUF ^e 1 the buffered mode is pro-
grammed In buffered mode SP EN be-
comes an enable output and the master
slave determination is by M S
M S If buffered mode is selected M S ^e 1
means the 8259A is programmed to be a
AEOI
mPM
master M S ^e 0 means the 8259A is pro-
grammed to be a slave If BUF ^e 0 M S
has no function
If AEOI ^e 1 the automatic end of interrupt
mode is programmed
Microprocessor mode mPM ^e 0 sets the
8259A for MCS-80 85 system operation
mPM ^e 1 sets the 8259A for 8086 system
operation
231468 – 10
Figure 7 Initialization Command Word Format
231468 – 11
11