Programming 8259

Programming 8259: The Programming 8259 requires two types of command words. Initialization Command Words (ICWs) and Operational Command Words (OCWs). The Programming 8259 can be initialized with four ICWs; the first two are compulsory, and the other two are optional based on the modes being used. These words must be issued in a given sequence. […]

Interfacing 8259 with 8085

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 F0H or F1H on the address bus. The A0 input of the 8259A is used to select one of the […]

Features of 8259 Programmable Interrupt Controller

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 pin. 2. It is possible to locate vector table for these additional interrupts any where in the memory map. However, […]

Interfacing of 8257 with 8085

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, indicating I/O bus cycle. In master mode DMA controller: (8257) generates MEMR,MEMW, IOR and IOW signals to control the data […]

Operating Modes of 8257

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. In this, channel being serviced gets the lowest priority and the channel next to it gets the highest priority as […]