draw and explain block diagram of dma controller pdf Thursday, May 13, 2021 5:38:19 AM

Draw And Explain Block Diagram Of Dma Controller Pdf

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Direct memory access DMA is a feature of computer systems that allows certain hardware subsystems to access main system memory random-access memory independent of the central processing unit CPU. Many hardware systems use DMA, including disk drive controllers, graphics cards , network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors.

Direct Memory Access (DMA) in Computer Architecture

Data Bus D 0 -D 7 : These are bi-directional tri-state signals connected to the system data bus. When CPU is having control of system bus it can access contents of address register, status register, mode set register, and a terminal count register and it can also program, control registers of DMA controller, through the data bus.

During DMA cycles these lines are used to send the most significant bytes of the memory address from one of the. In the idle cycle they are inputs and used by the CPU to address the register to be loaded or read. In the Active cycle they output the lower 4 bits of the address for DMA operation. A 4 -A 7 are unidirectional lines, provide 4-bits of address during DMA service. Address Enable AEN : This active high signal enables the 8-bit latch containing the upper 8-address bits onto the system address bus.

In the active cycle IOR signal is used to access data from a peripheral and IOW signal is used to send data to the peripheral. Reset : This active high signal clears, the command, status, request and temporary registers. After reset the device is in the idle cycle. It is used for requesting CPU to get the control of system bus. MARK always occurs at all multiplies of cycles from the end of the data block. It is a tri-state, bi-directional, eight bit buffer which interfaces the to the system data bus.

In the slave mode, it is used to transfer data between microprocessor and internal registers of In master mode, it is used to send higher byte address A 8 -A 15 on the data bus. During DMA cycles i.

Each channel has two sixteen bit registers:. DMA address register : Fig. It specifies the address of the first memory location to be accessed.

It is necessary to load valid memory address in the DMA address register before channel is enabled. Terminal Count Register : Fig. Note : N is number of bytes to be transferred. The value loaded into the low order 14 bits C 13 — C 0 of the terminal count register specifies the number of DMA cycles minus one before the terminal count TC output is activated. Therefore, for N number of desired DMA cycles it is necessary to load the value N-1 into the low order bits of the terminal count register.

The most significant 2 bits of the terminal count register specifies the type of DMA operation to be performed.

It is necessary to load count for DMA cycles and operational code for valid DMA cycle in the terminal count register before channel is enabled. It consists of mode set register and status register. Mode set register is programmed by the CPU to configure whereas the status register is read by CPU to check which channels have reached a terminal count condition and status of update flag. Least significant four bits of mode set register, when set, enable each of the four DMA channels.

Most significant four bits allow four different options for the Pin Diagram. It is cleared by the RESET input, thus disabling all options, inhibiting all channels, and preventing bus conflicts on power-up.

As said earlier, it indicates which channels have reached a terminal count condition and includes the update flag described previously. The TC status bit, if one, indicates terminal count has been reached for that channel.

TC bit remains set until the status register is read or the is reset. The update flag , however, is not affected by a status read operation. The update flag bit, if one, indicates CPU that is executing update cycle. In update cycle loads parameters in channel 3 to channel 2. Skip to content.

Direct Memory Access (DMA) in Computer Architecture

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.

Data Bus D 0 -D 7 : These are bi-directional tri-state signals connected to the system data bus. When CPU is having control of system bus it can access contents of address register, status register, mode set register, and a terminal count register and it can also program, control registers of DMA controller, through the data bus. During DMA cycles these lines are used to send the most significant bytes of the memory address from one of the. In the idle cycle they are inputs and used by the CPU to address the register to be loaded or read. In the Active cycle they output the lower 4 bits of the address for DMA operation. A 4 -A 7 are unidirectional lines, provide 4-bits of address during DMA service.

We use Cookies to give you best experience on our website. By using our website and services, you expressly agree to the placement of our performance, functionality and advertising cookies. Please see our Privacy Policy for more information. Register Block The and non- modes have different types of registers. The mode ,. Block Diagram Figure 1.

Direct memory access

For the execution of a computer program, it requires the synchronous working of more than one component of a computer. Usually, processors control all the process of transferring data, right from initiating the transfer to the storage of data at the destination. This adds load on the processor and most of the time it stays in the ideal state, thus decreasing the efficiency of the system.

It handles all the input-output operations of the computer system. Input or output devices that are connected to computer are called peripheral devices. These devices are designed to read information into or out of the memory unit upon command from the CPU and are considered to be the part of computer system. These devices are also called peripherals.

Microprocessor - 8257 DMA Controller

For the execution of a computer program, it requires the synchronous working of more than one component of a computer. Usually, processors control all the process of transferring data, right from initiating the transfer to the storage of data at the destination. This adds load on the processor and most of the time it stays in the ideal state, thus decreasing the efficiency of the system. DMA controller transfers data with minimal intervention of the processor. The term DMA stands for direct memory access.

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Fig Block diagram of DMA Controller. Fig DMA Control Operation. DMA Operation: Direct Memory Access involves transfer of data between I/O devices.


How DMA Operations are Performed?

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