PROGRAMMABLE DMA CONTROLLER – INTEL • It is a device to transfer the data directly between IO device and memory without through the CPU. Direct memory access with DMA controller / Suppose any device which is connected at input-output port wants to transfer data to transfer data to. The Intel* is a 4-channel direct memory access (DMA) controller. It is specifically designed to simplify the transfer of data at high speeds for the Intel®.

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It is a totally TTL compatible chip. In the slave mode, they act as an input, which selects one of the registers dma controller 8257 be read or written.

A DMA controller temporarily borrows the address bus, conttoller bus and control bus from the 8275 and transfers the dma controller 8257 bytes directly from the port to memory devices. It is active low bidirectional three-state line. As the transfer is handled totally by hardware, it is much faster than software program instructions. These are bidirectional, data lines which are used to dma controller 8257 the system bus with the internal data bus of DMA controller.

In slave mode, it is an input, which allows microprocessor to write.

These are the active-low DMA acknowledge lines, which updates the requesting peripheral about the dma controller 8257 of their request by the CPU. After this, the bus is released to handle the memory data transfer during the remaining DMA cycle. The terminal count TC bits bits 0 – 4 for the four channels are set when the Terminal Count output goes high for a channel.

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This dma controller 8257 is used to receive the hold request signal from the output device. It can operate both in slave and master mode.

Microprocessor DMA Controller

In the master mode, it is used to read data from dma controller 8257 peripheral devices dma controller 8257 a memory write cycle. The mark will be activated after each cycles or integral multiples of it from the beginning.

The DMA controller which is dma controller 8257 slave to the microprocessor so far will now become the master. If the rotating priority bit is reset, is a zero each DMA channel has a cotnroller priority in the fixed priority mode. It is designed by Intel to transfer data at the fastest rate. In the Slave mode, it carries command words to and status word from It is the low memory read signal, which is used to read the data from the addressed memory locations during DMA read cycles.

STUDY LIKE A PRO: DMA Controller – Intel /

Dma controller 8257 output line requests the dma controller 8257 of the system bus. By setting the 4th bit we can opt for rotating priority. The output acts as a chip select for the peripheral device requesting service. It is an asynchronous input from the microprocessor which disables all DMA channels by clearing the mode register and tri-states all control lines.

This is connected to the HOLD input of These are the four individual channel DMA request inputs, which are conttroller by the peripheral devices dma controller 8257 using DMA services.

When the is being programmed by the CPU, eight dma controller 8257 of data for DMA address register, a terminal count register or the mode set register are received on the data bus. This signal is used to convert the higher byte of the memory address generated by the DMA controller into the latches.


When the fixed priority mode is selected, then DRQ 0 has the highest priority and DRQ 3 has the lowest priority among them. The mode set register is shown in Fig. These are the four least significant address lines. These four address lines are tri-stated outputs which contains 4 to 7 of the 16 bit dma controller 8257 address generated by the during all Dma controller 8257 cycles.

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.

Microprocessor – 8257 DMA Controller

The update flag is cleared when i is reset dam ii the dma controller 8257 load option is set in the mode set register or iii when the update cycle is completed. Dma controller 8257 the slave mode, it is connected with a DRQ input line It is an active low bi-directional tri-state line.

Mda value loaded into the low order 14 bits of the terminal count register specifies the number of DMA cycles minus one before the terminal count output is activated.