Pin Diagram of 8279: Fig. 14.83 shows functional and pin diagram of 8279. It is a 40 pin device and looking at Fig. 14.83 (a) we can see that these pins are divided in four…

8259 Programmable Interrupt Controller: The 8259 Programmable Interrupt Controller requires two types of command words. Initialization Command Words (ICWs) and Operational Command Words (OCWs). The 8259 Programmable Interrupt Controller can be initialized with four ICWs;…

Interfacing 8259 with 8085: Fig. 14.72 shows Interfacing 8259 with 8085 microprocessor system. Addressing of 8259A : The 74LS138 address decoder will assert the CS input of the 8259A when an I/O base address is…

8259 Block Diagram: Fig. 14.71 shows the internal 8259 Block Diagram. It includes eight blocks : data bus buffer, read/write logic, control logic, three registers (IRR, ISR and IMR), priority resolver, and cascade buffer. Data…

Features of 8259 Programmable Interrupt Controller: The Features of 8259 Programmable Interrupt Controller are 1. It can manage eight priority interrupts. This is equivalent to providing eight interrupt pins on the processor in place of INTR…

Interfacing of 8257 with 8085: Fig. 14.68 shows the interfacing of 8257 with 8085 in I/O mapped I/O technique. In slave mode, RD and WR signals are activated by CPU when IO/M signal is high,…

Operating Modes of 8257: The Operating Modes of 8257 can be programmed to operate in following modes : Rotating Priority Mode : In rotating priority mode, the priority of the channels has a circular sequence.…

8257 Pin Diagram: Fig. 14.61 shows 8257 Pin Diagram. Data Bus (D0-D7) : These are bi-directional tri-state signals connected to the system data bus. When CPU is having control of system bus it can access…