
390 THE x86 MICROPROCESSORS
Solution
IN AL, 0C2H ;to read IMR, READ OCW1
MOV AL, 6AH ;write OCW3 for reading IRR
IN AL, 0C0H ;read IRR
MOV BL, AL ;save IRR in BL
MOV AL, 69H ;write OCW3 for reading ISR
IN AL, 0C0H ;read ISR
MOV CL, AL ;save it in CL
Note e 8259 is a complex chip and for fi ner details, the data sheet of the chip is to be
referred to.
10.4 | Cascade Mode
e 8259 can be easily interconnected in a system of one master with up to eight slaves to
handle up to 64 priority levels. e master controls the slaves through the 3 line cascade bus. e
cascade bus acts like chip selects to the slaves during the INTA sequence. ...