5 Mar / DMA – DIRECT MEMORY ACCESS. DMA requires another processor – The DMA Controller or DMACto generate the memory. What is DMA controller? DMA stands for 4-channel Direct Memory Access. It is specially designed by Intel for data transfer at the highest speed. Direct memory access with DMA controller / Suppose any device which is connected at input-output port wants to transfer data to transfer data to.

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Have you ever lie on your resume? After this, the bus is released to handle the memory data transfer during the remaining DMA cycle. Embedded C Interview Questions.

Microprocessor – 8257 DMA Controller

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These are the active-low DMA acknowledge lines, which updates the requesting peripheral about the status of their request by the CPU. It is an cojtroller bidirectional tri-state input line, which is used by the CPU to read internal registers of in the Slave mode. These are bidirectional, data lines which help to interface the system bus with the internal data bus of DMA controller.

Now the HLDA signal is activated. The mode set register is shown in Fig.

Microprocessor DMA Controller

In the slave mode, it is connected with a DRQ input line It is specially designed by Intel for data transfer at the highest speed. When the is being programmed by the CPU, eight bits of data for DMA address register, a terminal count register or the mode set register are received on the data bus. There are also two 8-bit registers one is the mode set register and the other is status register. But in the rotating priority mode the priority of the controlller has a circular sequence and after each DMA cycle, the priority of each channel changes.

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This signal is used to convert the higher byte of the memory address generated by the DMA controller into the latches. It is an asynchronous input from the microprocessor which disables all DMA channels by clearing the mode register and tri-states all control lines.

In Direct Memory Access technique, the data transfer takes place without the intervention of CPU, so there must be a controller circuit which is programmable and which can perform the data transfer effectively. When is operating as Master, during a DMA cycle, it gains control over the system buses. In the master mode, the lines which are used to send higher byte of the generated address are sent to the latch. In the contrkller mode they are inputs, which select one of the dmaa to be read or programmed.

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In the slave mode, they perform as an input, which selects one of the registers to be read or written. This is the clock output of the microprocessor. Microprocessor Interview Questions. These are the contrpller individual channel DMA request inputs, which are used by the peripheral controlleer for using DMA services. How to design your resume?


It is designed by Intel to transfer data at the fastest rate. In the master mode, it is used to read data from the peripheral devices during a memory write cycle.

Microprocessor 8257 DMA Controller Microprocessor

Rise in Demand for Talent Here’s how to train middle managers This is how banks are wooing startups Nokia to cut thousands of jobs. It is the active-low three state signal which is used to write the data to the addressed memory location during DMA write operation. These are the four least significant address lines. This block controls the sequence operations during all DMA cycles by generating the appropriate control signals and 16 bit address that specifies the memory relations to be accessed.

It is the active-low three state signal which is used to write the data to the addressed memory location during DMA write operation. When the rotating priority mode is selected, then DRQ0 will get the highest priority and DRQ3 will get the lowest priority among them.

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