8257 DMA CONTROLLER PDF

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You can change your ad preferences anytime. Upcoming SlideShare. Like this presentation? Why not share! Embed Size px. Start on. Show related SlideShares at end. WordPress Shortcode. ShivamSood22 Follow. Published in: Engineering. Full Name Comment goes here. Are you sure you want to Yes No. Rishikesh Shete. Jeena Kunnel. Show More. No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. No notes for slide. Microprocessor then executes the program until it needs to read a block of data from the disk.

Asserting the IOR signals enables the disk controller to output the data from the disk on the data bus and MEMW signal enables the addressed memory to accept data form the data bus. Each channel can be programmed independently to transfer up to 64kb of data by DMA.

The priority logic can be programmed to work in two modes, either in fixed mode or rotating priority mode. The functional block diagram consists of 1. DMA channels 2. Data bus buffer 3. Control logic 5. Mode set Register 6. Status Register Eight bits of data for DMA address register, terminal count register or the Mode Set register are received on the data bus.

After this, the bus is released to handle the memory data transfer during the remaining DMA cycle. HRQ must conform to specified setup and hold times. So this pin is used to split data and address line from the DMA. So we need to demultiplex these data lines for which AEN pin is used. When the rotating priority mode is selected, then DRQ0 will get the highest priority and DRQ3 will get the lowest priority among them.

These lines can also act as strobe lines for the requesting devices. In the master mode, the lines which are used to send higher byte of the generated address are sent to the latch. In the master mode, it also helps in reading the data from the peripheral devices during a memory write cycle. In the master mode, it is used to load the data to the peripheral devices during DMA memory read cycle. In the slave mode, they perform as an input, which selects one of the registers to be read or written.

In the master mode, they are the outputs which contain four least significant memory address output lines produced by In the slave mode, it is connected with a DRQ input line You just clipped your first slide!

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Microprocessor 8257 DMA Controller - Microprocessor

It holds the ability to directly access the main memory for read or write operation. DMA controller was designed by Intel , to have the fastest data transfer rate with less processor utilization. We know in order to execute an operation, the microprocessor first fetches the instruction and then decodes it, then further execute it. But individually if the processor is performing all the task inside the system then it unnecessarily keeps the processor busy all the time. So, to enhance the performance of the processor, an external device is used that can manage data transfer operation between peripherals and memory with least CPU utilization.

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Direct Memory Access (DMA) in Computer Architecture

For the execution of a computer program, it requires the synchronous working of more than one component of a computer. Usually, processors control all the process of transferring data, right from initiating the transfer to the storage of data at the destination. This adds load on the processor and most of the time it stays in the ideal state, thus decreasing the efficiency of the system. DMA controller transfers data with minimal intervention of the processor. The term DMA stands for direct memory access. The hardware device used for direct memory access is called the DMA controller.

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Direct memory access with DMA controller 8257/8237

Suppose any device which is connected at input-output port wants to transfer data to transfer data to memory, first of all it will send input-output port address and control signal, input-output read to input-output port, then it will send memory address and memory write signal to memory where data has to be transferred. In normal input-output technique the processor becomes busy in checking whether any input-output operation is completed or not for next input-output operation, therefore this technique is slow. This problem of slow data transfer between input-output port and memory or between two memory is avoided by implementing Direct Memory Access DMA technique. Suppose a floppy drive which is connected at input-output port wants to transfer data to memory, the following steps are performed:. GeeksforGeeks has prepared a complete interview preparation course with premium videos, theory, practice problems, TA support and many more features. Please refer Placement for details.

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DMA Controller

It is designed by Intel to transfer data at the fastest rate. Then the microprocessor tri-states all the data bus, address bus, and control bus. These are the four individual channel DMA request inputs, which are used by the peripheral devices for using DMA services. When the fixed priority mode is selected, then DRQ 0 has the highest priority and DRQ 3 has the lowest priority among them. These are the active-low DMA acknowledge lines, which updates the requesting peripheral about the status of their request by the CPU. These lines can also act as strobe lines for the requesting devices.

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