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It is designed by Intel to transfer data at the fastest rate. Then the microprocessor tri-states all the data bus, address bus, and control bus. These are the four individual channel DMA request inputs, which are used by the peripheral devices for using DMA services. When the fixed priority mode is selected, then DRQ 0 has the highest priority and DRQ 3 has the lowest priority among them.
These are the active-low DMA acknowledge lines, which updates the requesting peripheral about the status of their request by the CPU. These lines can also act as strobe lines for the requesting devices. These are bidirectional, data lines which are used to interface the system bus with the internal data bus of DMA controller. In the Slave mode, it carries command words to and status word from In the master mode, these lines are used to send higher byte of the generated address to the latch.
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. In the master mode, it is used to read data from the peripheral devices during a memory write cycle. In the master mode, it is used to load the data to the peripheral devices during DMA memory read cycle. These are the four least significant address lines. In the slave mode, they act as an input, which selects one of the registers to be read or written.
In the master mode, they are the four least significant memory address output lines generated by It is an active-low chip select line. This signal is used to receive the hold request signal from the output device.
In the slave mode, it is connected with a DRQ input line 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. 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 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. The mark will be activated after each cycles or integral multiples of it from the beginning. Previous Page. Next Page. Previous Page Print Page.
Description of the pins of 8257
Suppose any device which is connected at input-output port wants to transfer data to transfer data to memory, first of all it will send input-output port address and control signal, input-output read to input-output port, then it will send memory address and memory write signal to memory where data has to be transferred. In normal input-output technique the processor becomes busy in checking whether any input-output operation is completed or not for next input-output operation, therefore this technique is slow. This problem of slow data transfer between input-output port and memory or between two memory is avoided by implementing Direct Memory Access DMA technique. Suppose a floppy drive which is connected at input-output port wants to transfer data to memory, the following steps are performed:. GeeksforGeeks has prepared a complete interview preparation course with premium videos, theory, practice problems, TA support and many more features. Please refer Placement for details. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.
Direct memory access with DMA controller 8257/8237
Uses the fixed priority method. Channel 0 will have the highest and Channel 3 will have the lowest priority. Description of the pins of Microcontroller Microprocessor Fig: The block diagram showing the interfacing of in a based system of Anvi Jain. Previous Page Print Page. Next Page.