Microprocessors and Microcontrollers: Unit IV: (b) Programmable Interrupt Controller (PIC) - 8259
8259A Interfacing with 8085
Review Questions : 1. Draw and explain the interfacing of 8259 with 8085. 2. How 8259 is interfaced with 8085 or 8051 ?
8259A Interfacing with 8085
Fig.
9.7.1 shows that how an 8259A can be interfaced with the 8085 microprocessor
system.
Fig.
9.7.1 Interface to 8085 system bus
Addressing
of 8259A :
The
74LS138 address decoder will assert the 
input of the 8259A when an I/O
base address is F0H or F1H on the address bus. The A0 input of the
8259A is used to select one of the two internal addresses in the device. A0
of the 8259A is connected to system line A0. So the system addresses
for the two internal addresses are F0H and F1H. The data lines of an 8259A are
connected to the AD0-AD7 of the system data bus, 
and 
signals are connected to the system and lines.
The interrupt request signal INT from the 8259A is connected to the INTR input
of the 8085 and 
from the 8085 is connected to of the 8259A.
As we are using single 8259A in the system, 
pin is tied high and CAS0-CAS2
lines are left open. The eight IR inputs are available for interrupt signals.
Note
Unused
IR inputs should be tied to ground so that a noise pulse cannot accidently
cause an interrupt.
Review Questions
1. Draw and explain the interfacing of 8259 with 8085.
2. How 8259 is interfaced with 8085 or 8051 ?
Microprocessors and Microcontrollers: Unit IV: (b) Programmable Interrupt Controller (PIC) - 8259 : Tag: : - 8259A Interfacing with 8085