DMA Controller is a peripheral core for microprocessor systems. It controls data transfer between the main memory and the external systems with limited. Intel is a direct memory access (DMA) controller, a part of the MCS 85 microprocessor . and ) have an CPU and an 8-bit system bus architecture; the latter interfaces directly to the , but the has a bit address bus. Direct memory access with DMA controller / Step After accepting the DMA service request from the DMAC, the CPU will send hold acknowledgement (HLDA) to More related articles in Computer Organization & Architecture.

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Auto-initialization may be programmed in this mode. In auto initialize mode the address and count values are restored upon reception of an end of process EOP signal. This page was last edited on 21 Mayat Memory-to-memory transfer can be performed.

This signal is used to convert the higher byte of the memory address generated by the DMA controller into the latches.

It is an active-low chip select line. Each channel is capable of addressing a full 64k-byte section of memory and can transfer architecturee to 64k bytes with a single programming.

Block Diagram of 8237

Because the memory-to-memory DMA mode operates by transferring a byte from the source memory location to an internal temporary 8-bit register in the and then from the temporary register to the destination memory location, this mode could not be used for bit memory-to-memory DMA, as the temporary register is not large enough.


In the slave mode, they act as an input, which selects one of the registers to be read or written. In the master mode, it is used to read data from the peripheral devices during a memory write cycle.

DMA transfers on any channel still cannot cross a 64 KiB boundary.

Block Diagram of

Then the microprocessor tri-states all the data bus, address bus, and control bus. Retrieved from ” https: In the slave mode, it is connected with a DRQ input line Consequently, a limitation on these machines is that the DMA controllers with their companion address “page” extension registers only can address 16 MiB of memory, according to the original design oriented around the CPU, which itself has this same addressing limitation. Although this device may not appear as a discrete component in modern personal computer systems, it does appear within system controller chip sets.

In single mode only one byte is transferred per request.

In an AT-class PC, all eight of the address augmentation registers are 8 bits wide, so that full bit addresses—the size of the address bus—can be specified.

Additionally, memory-to-memory bit DMA would require use of channel 4, conflicting with its use to cascade the that handles the 8-bit DMA channels. From Wikipedia, the free encyclopedia. When the counting register reaches zero, the terminal count TC signal is sent to the card.

When the fixed priority mode is selected, then DRQ 0 has the highest priority and DRQ 3 has the lowest priority among them. 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. It is used to repeat the last transfer.


For example, the P ISP integrated system controlleer controller has two DMA internal controllers programmed almost exactly like the In the Slave mode, it carries command words to and status word from Views Read Edit View history. The operates in four different modes, depending upon the number of bytes transferred per cycle and number of ICs used:.

For every transfer, the counting register is decremented and address is incremented or decremented depending on programming. These are bidirectional, data lines which are used to interface the system bus with the internal data bus of DMA controller.

8237 DMA Controller

These lines can also act as strobe lines for the requesting devices. 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 transfer continues until end of process EOP either internal or external is activated which will trigger terminal count TC to the card. In the master mode, these lines are used to send higher byte of the generated address to the latch. The is a four-channel arfhitecture that can be expanded to include any number of DMA channel architectture. In the master mode, they are the four least significant memory address output lines generated by