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 A Multimode Direct Memory Access (DMA) Controller is a peripheral three basic transfer modes allow programmability of the types of DMA service by . DMA Controller is a peripheral core for microprocessor systems. It controls data transfer between the main memory and the external systems with limited.

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For example, the P ISP integrated system peripheral controller has two DMA internal controllers programmed almost exactly like the When the counting register reaches zero, the terminal count TC signal is sent to the card.

Views Read Edit View history. 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.

The IBM PC and PC XT models machine types and have an CPU and an 8-bit system bus architecture; the latter interfaces directly to thebut the has a bit address bus, so four additional 4-bit address latches, one for each DMA channel, are added alongside the to augment the address counters.

The is a four-channel device that can be expanded to include any number of DMA channel inputs. However, because these external latches are separate from the address counters, they are never automatically incremented or decremented during DMA operations, making it impossible to perform a DMA operation across a 64 KiB address boundary.


As a member of the Intel MCS device family, the is an 8-bit device with bit addressing. This technique is called “bounce buffer”. This happens without any CPU intervention. From Wikipedia, the free encyclopedia. For this mode of transfer, the width of the data bus is essentially immaterial to the as long as it is connected to a data bus at least 8 bits wide, for programming the registers.

This means data can be transferred from one memory device to another memory device.

In auto initialize mode the address and count values are restored upon reception of an end of process EOP signal. The channel 0 Current Address register is the source for the data transfer and channel 1 and the transfer terminates when Current Word Count register becomes 0.

DMA: What it is and how it works

Although this device may not appear as a discrete component in modern personal computer systems, it does appear within system controller chip sets.

Memory-to-memory transfer can be performed. By using this site, you agree to the Terms of Use and Privacy Policy.

For every transfer, the counting register is decremented and address is incremented or decremented depending on programming. The is capable of DMA transfers at rates conhroller up to 1.

Introduction of 8237

Retrieved from ” https: Auto-initialization may be programmed in this mode. Like the firstit is contdoller with four address-extension registers. It is used to repeat the last transfer. The transfer continues until end of process EOP either internal or external is activated which will trigger terminal count TC to the card.

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. So that it can address bit words, it is connected to the address bus in such a way that it counts even addresses 0, 2, 4, Because the memory-to-memory DMA mode operates by transferring a byte from the source dmw location to an internal temporary 8-bit register in the and then cma 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.


DMA transfers on any channel still cannot cross a 64 KiB boundary. In single mode only one byte is transferred per request. 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.

Intel 8237

The operates in four different modes, depending upon the number of bytes transferred per cycle and number of ICs used:. In general, it loses any overall speed benefit associated with DMA, but it may be necessary if a peripheral requires to be accessed by DMA due to either demanding timing requirements or hardware interface inflexibility.

At the end of transfer an auto initialize will occur configured to do so. Each channel is capable of addressing a full 64k-byte section of memory and can transfer up to 64k bytes with a single programming. This page was last edited on 21 Mayat

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