Explain 8259 Pin Diagram.

The 8259A adds 8 vectored priority encoded interrupts to the microprocessor. It can be expanded to 64 interrupt requests by using one master 8259A and 8 slave units. CS and WR must be decoded. Other connections are direct to microprocessor.  The pins D7 - D0: the bidirectional data connection, IR7 - IR0: Interrupt request, used to request an interrupt & connect to a slave in a system with multiple 8259A.

WR: Attaches to a write strobe signal (lower or upper into a 16 bit system) ,

 RD: Attaches to the IORC signal, 

INT:  Attaches to the INTR pin on the microprocessor from the master and is Attached to a IR pin onto a slave and 

INTA: Attaches to the INTA pin onto the microprocessor.

Within a system only the master INTA signal is attached

Fig: 8259 Pin Diagram