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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DMA Controller 8257

The request priorities are decided internally. In the master mode, they are outputs, which constitute the most significant 4 bits of the 16 bit memory address generated by the dma controller 8257 By setting the 4th bit we can opt for rotating priority. It is an asynchronous input from the microprocessor which disables all DMA channels by clearing the mode register and tri-states all control lines.

These are the four least significant address lines. It is the low memory read signal, which is used to read the data from the addressed memory locations during DMA read cycles. dma controller 8257


Each channel has two 16 bit registers. In the master mode, it is used to load the data to the peripheral devices during DMA memory read cycle. Dma controller 8257 functional block diagram is shown below. Now the HLDA signal is activated. In slave mode, it is an input, which allows microprocessor to write. 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 dma controller 8257 the data transfer effectively.

It is designed by Intel to transfer data at the fastest rate.

Three state bidirectional, 8 bit buffer interfaces the to the system data bus. The DMA address register is loaded with the address of the first memory location to be accessed.

As the transfer is handled totally by hardware, it is dma controller 8257 faster than software program instructions. These lines can also act as strobe lines for the requesting devices.

Newer Post Older Post Home. The update flag is cleared when i is reset or controler the auto load option dma controller 8257 set in the mode set register or dma controller 8257 when the update cycle is completed. It is the active-low three state signal which is used to write the data to the addressed memory location during DMA write operation. After this, the bus is released to handle the memory data transfer during the remaining DMA cycle.

Microprocessor – 8257 DMA Controller

In the Slave mode, it carries command words to and status word from It is the hold acknowledgement signal which indicates the DMA controller that the bus has been granted to the requesting peripheral by the CPU when it is set to 1.

The 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. This register is used to set the mode of operation of In dma controller 8257 master mode, dma controller 8257 is used to read data from the peripheral devices during a memory write cycle.

Intel is a programmable, 4-channel direct memory access controller i.

Microprocessor DMA Controller

But in the rotating dma controller 8257 mode the priority of the channels has a circular sequence and after each DMA cycle, the priority of each channel changes. This is the clock output of the microprocessor. The TC bits in the status word are cleared when the status word is read or when the receives a Reset dma controller 8257. These are the four individual channel DMA request inputs, which are used by the peripheral devices for using DMA services. 88257 the rotating priority bit is reset, is a zero each DMA channel has a fixed priority in the fixed priority mode.

A DMA controller dma controller 8257 borrows the address bus, data bus and control bus from the microprocessor and transfers the data bytes directly from the port to memory devices. In the slave mode they are inputs, which select one of the registers to be read or programmed.

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.