Interrupt Controller (8259A)
The special mask mode is useful when one or more interrupts are
masked. If for any reason an input is masked while it is being
serviced, the lower priority interrupts are disabled. However, it is
possible to enable the lower priority interrupt with the special mask
mode. In this mode, the lower priority lines are enabled until the
special mask mode is reset. Higher priorities are not affected.
Poll Mode
In this mode, the CPU internal Interrupt Enable flip-flop is clear
(interrupts disabled) and a software subroutine is used to initiate a poll
command. In the poll mode, the addressed PIC treats an I/O Read
Control as an interrupt acknowledge, sets its In-Service flip-flop if
there is a pending interrupt request, and reads the priority level. This
mode is useful if there is a common service routine for several
devices.
In poll mode, the word enabled onto the data bus during RD* is:
D7
D6
D5
D4
D3
D2
D1
D0
A
—
—
—
—
W2
W1
W0
where W0-W2 are binary code of the highest priority level requesting
service, and A is equal to a "1" if there is an interrupt.
Interrupt Triggering
Two ways of sensing an active interrupt request are a level sensitive
input or an edge sensitive input. The 8259A gives you the capability
for either method with the edge-triggered mode and the level-
triggered mode. Selection of one of these interrupt triggering methods
is done during the programmed initialization of the 8259A.
12-27
Содержание ZT 8809A
Страница 15: ...Tables Table B 9 J5 Pin Assignments B 17 Table B 10 J6 Pin Assignments B 18 Table B 11 J7 Pin Assignments B 19...
Страница 334: ...Jumper Configurations W49 W48 A W47 B A B W37 W66 A W50 B C J7 W67 Figure A 11 W37 W47 50 W66 W67 Jumper Blocks A 34...
Страница 346: ...Jumper Configurations W61 W60 W62 W63 W64 A B A B W65 Figure A 13 W60 W65 Jumper Block A 46...