Explain the 8259 microprocessor.

8259:

The 8259A adds 8 vectored priority encoded interrupts to the microprocessor. This can be expanded to 64 interrupt requests with using one master 8259A and 8 slave units. CS and WR should be decoded. Other connections are direct to microprocessor.  The workings of pins are given here:

Pins D7 to D0: bidirectional data connection pins,

IR7 to IR0: Interrupt request, utilized to request an interrupt and connect to a slave in a system along with multiple 8259A.

WR: It connects to a write strobe signal (upper or lower in a 16 bit system) , 

RD: It connects to the IORC signal, 

INT: it Connects to the INTR pin on the microprocessor by the master and it is connected to a IR pin on a slave and 

INTA: It connects to the INTA pin on the microprocessor.  Within a system only the master INTA signal is associated

A0: it selects different command words along with in the 8259A,

CS: Chip select - It enables the 8259A for programming and control, 

SP/EN: Slave Program (that is 1 for master, 0 for slave)/Enable Buffer (as controls the data bus transceivers into a large microprocessor based system while in buffered mode) and 

CAS2-CAS0: It used as outputs from the master to the slaves in cascaded systems.

Figure: 8259 Block Diagram