DMA stands for 4-channel Direct Memory Access. It is specially The following image shows the pin diagram of a DMA controller −. _pin. 3S. Da. Do,. Doack o. DOACK 1. Do,. Figure 1. Block Diagram. Figure 2. Pin Configuration. MO0€. HAO -. HLDA -. PAIORITY. AE SOLVEA. ME WW -. AEN -. ADSTE -. INTERNAL. Bus. MAAK. Figure 1. Block Diagram. Figure 2. Pin Configuration. 2-

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It consists of dagram set register and status register. It is designed by Intel to transfer data at the fastest rate. When the fixed priority mode is selected, then DRQ 0 has the highest priority and DRQ 3 has the lowest priority among them.

Pin Diagram of | Block Diagram of | Mode Set Register | Status Register

It is the active-low three state signal which is used to write the data to the addressed memory location during DMA write operation.

This signal is used to convert the higher byte of the memory address generated by the DMA controller into the latches. Interview Tips 5 ways to be authentic in an interview Pi to help you face your job interview Top 10 commonly asked BPO Interview questions 5 things you should never talk in any job interview Best job interview tips for job seekers 7 Tips to recruit the right candidates in 5 Important interview questions techies fumble most What are avoidable questions in an Interview?

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In the master mode, it is used to read data from the peripheral devices during a memory write cycle.

Microprocessor 8257 DMA Controller Microprocessor

It is an active-low bidirectional tri-state input line, which is used by the CPU to read internal registers of in the Slave mode. The value loaded into the low order 14 bits C 13 — C 0 of the terminal count register specifies the number of DMA cycles minus one before the terminal count TC output is activated.

These are the active-low DMA acknowledge lines, which updates the requesting peripheral about the status of their request by the CPU.

Interrupt Structure of Addressing Modes of Read This Tips for writing resume in slowdown What do employers look for in a resume? In the master mode, they are the four least significant memory address output lines generated by In the master mode, the lines which are used to send higher byte of the generated address are sent to the latch.

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Microprocessor – 8257 DMA Controller

It is specially designed by Intel for data transfer at the highest speed. It is an active-low chip select line.

N is number of bytes to be transferred. Therefore, for N number of desired DMA cycles it is necessary to load the value N-1 into the low diagran bits of the terminal count register.


The active high Hold Acknowledge from the CPU indicates that it has relinquished control of the system bus. Analog Communication Practice Tests.

These are the four individual channel DMA request inputs, which are used by the peripheral devices for using DMA services. Digital Logic Design Interview Questions. Survey Most Productive year for Staffing: In the master mode, it is used to load the data to the peripheral devices during DMA memory read cycle.

These are active low bi-directional signals. In the active cycle IOR signal is used to access data from a peripheral and IOW signal is used to send data to the peripheral.

It is the low memory read signal, which is used to read the data from the addressed memory locations during DMA read cycles. It is necessary to load valid memory address in the DMA address register before channel is enabled.

Supporting Circuits of Microprocessor. In the Slave diagrzm, command words are carried to and status words from TC bit remains set until the status register is read or the is reset.