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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In the master mode, it is used to load the dma controller 8257 to the peripheral devices during DMA memory read cycle. The output acts 88257 a chip select for the peripheral device requesting service.

When is operating as Master, during a DMA cycle, it gains control over the system buses. Each channel has two 16 bit registers.

The terminal count TC bits bits 0 – 4 for the four channels are dma controller 8257 when the Terminal Count output goes high controllrr a channel. These are the four least significant address controllfr. In the slave mode they are inputs, which select one of the registers to be read or programmed. The functional block diagram is shown below. It is designed by Intel to transfer data at the fastest rate. These are active low signals one for each of the four DMA channels. It is an asynchronous input from the microprocessor dma controller 8257 disables all DMA channels by clearing the mode register and tri-states all control lines.

In the slave mode, they act as an input, which selects one of the registers to be read or written. 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.

It can operate both in slave and master mode. Three state bidirectional, 8 bit buffer cojtroller the to the system data bus. These are bidirectional, data lines which are used to interface the system bus with the dma controller 8257 data bus of DMA controller.

By setting the 4th bit we can opt for rotating priority. These least dma controller 8257 four address lines are bidirectional. 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.

In slave mode, it dma controller 8257 an input, which allows microprocessor to write. This register is used to set the mode of 88257 of After this, the bus is released to handle the memory data transfer during the remaining DMA cycle. It is an active low bi-directional tri-state line. In the master mode, they are outputs, which constitute the most significant 4 bits of the 16 bit memory address generated by the This signal is used to receive the hold request signal from the output device.

A DMA controller can also transfer data from memory to a port. In the master mode, these lines are used to send higher byte of the generated address to the latch. This block controls the sequence operations during all DMA cycles by generating the appropriate control signals and 16 dma controller 8257 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 dma controller 8257. This is known as a DMA machine cycle, at the end of which, the number of bytes to be transferred is decremented by 1 in the count register and address register is incremented by 1 to point cnotroller the next memory address for dma controller 8257 transfer.

Microprocessor DMA Controller

dma controller 8257 These are the active-low DMA acknowledge lines, which updates the requesting peripheral about the status of their request by the CPU. 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.

The mode set register is shown in Fig. This is the clock output of the microprocessor.

Microprocessor – 8257 DMA Controller

In the master mode, they are the four least dmma memory address output lines generated by The DMA address register is loaded with the address of the first memory location to be accessed. The TC bits in the dma controller 8257 word dma controller 8257 cleared when the status word is read or when the receives a Reset input.

The request priorities are decided internally. There are also two 8-bit registers one is the mode set register and the other is status register.

DMA Controller

The mark will be activated after each cycles or integral multiples of it from the beginning. These lines can also act as strobe lines for the requesting devices. Then the microprocessor tri-states all the data bus, address bus, and dma controller 8257 bus. These four address lines are tri-stated outputs which contains 4 dma controller 8257 7 of the 16 bit memory address generated by the during all DMA cycles. But in the rotating priority mode the priority of the channels has a circular sequence and after each DMA cycle, the priority of each channel changes.

This is connected to the HOLD dma controller 8257 of The DMA controller which is a slave to the microprocessor so far will now become the master. As the transfer is handled totally by hardware, it is much faster than software program instructions.

The update flag is not affected by a status read operation. In dma controller 8257 Controlleg mode, dma controller 8257 carries command words to and status word from For this purpose Intel introduced the controller chip which is known as DMA controller. These are the four individual channel DMA request inputs, which are used by the peripheral devices for using DMA services.

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 dma controller 8257 set to 1. It is active low bidirectional three-state line.

This output line requests the control of the system bus. 2857 the master mode, it is used to read data from control,er peripheral devices during a memory write cycle. Newer Post Older Post Home. In the slave mode, it is connected with a DRQ input line