In this mode the system buses arc controlled by microprocessor and hence the microprocessor is connected to the system bus. In master mode becomes the bus master and hence the microprocessor is isolated from the system bus. This isolation is done by AEN signal. In minimum configuration, DMA controller is used to transfer the data. The peripheral chips are interface as normal 10 ports. Figure shows the interfacing of DMA controller with
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In this mode the system buses arc controlled by microprocessor and hence the microprocessor is connected to the system bus. In master mode becomes the bus master and hence the microprocessor is isolated from the system bus. This isolation is done by AEN signal.
In minimum configuration, DMA controller is used to transfer the data. The peripheral chips are interface as normal 10 ports. Figure shows the interfacing of DMA controller with The outputs only bit memory address but not the complete bit address of The is not compatible with in its maximum mode configuration.
So if is to be interfaced with DMA controller, then 10 processor is required. It shares the bus buffers and system controller of the host system. Different data transfer modes of DMA controller: The is in the idle cycle if there is no pending request or the is waiting for a request from one of the DMA channels.
In the active cycle, the actual data transfer takes place in one of the following transfer modes as is programmed. Single Transfer Mode: In this mode, the device transfers only one byte per request. The word count is decremented and the address is decremented or incremented depending on programming after each such transfer. The Terminal Count TC state is reached when the count becomes zero.
Auto-initialization may be programmed in this mode. Cascade Mode: In this mode, more than one can be connected together to provide more than four DMA channels. The priorities of the DMA requests may be preserved at each level.
The first device is only used for prioritizing the additional devices slave s , and it does not generate any address or control signal of its own. All other outputs of the host are disabled. Memory to memory Transfer: To perform the transfer of a block of data from one set of memory address to another one, this transfer mode is used. Programming the corresponding mode bit in the command word, sets the channel 0 and I to operate as source and destination channels, respectively.
The transfer is initialized by setting the DREQ0 using software commands. The channel 0 current address register acts as a source pointer. The byte read from the memory is stored in an internal temporary register of The channel 1 current address register acts as a destination pointer to write the data from the temporary register to the destination memory location.
The pointers are automatically incremented or decremented, depending upon the programming. The channel 1 word count register is used as a counter and is decremented after each transfer. The also responds to external EOP signals to terminate the service. This feature may be used to scan a block of data for a byte. When a match is found the process may be terminated using the external EOP. Under all these transfer modes, the carries out three basic transfers namely, write transfer, read transfer and verify transfer.
In verify transfers, the works in the same way as the read or write transfer but does not generate any control signal.
Microprocessor - 8257 DMA Controller
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. Each channel has bit address and bit counter. Each channel can transfer data up to 64kb. Each channel can be programmed independently. Each channel can perform read transfer, write transfer and verify transfer operations. It generates MARK signal to the peripheral device that bytes have been transferred.