Intel 386 Manual do Utilizador descarregar pdf (Página 349)

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Intel386™ EX EMBEDDED MICROPROCESSOR USER’S MANUAL

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transfer is suspended and the channel waits for the request input to be

reactivated before it continues.

12.2.7.1 Single Data-transfer Mode

In single data-transfer mode, a DMA request causes the channel to gain bus control. The channel

transfers data (a byte or a word), decrements the buffer byte count (by 1 for byte transfers and 2

for word transfers), then relinquishes bus control. The channel will then Autoinitialize if it has

been programmed to do so. The channel continues to operate in this manner until the buffer trans-

fer is complete or terminated. In this mode, the channel gives up bus control after every data trans-

fer and must regain bus control (through priority arbitration) before every data transfer. The

channel’s buffer-transfer mode determines whether the channel becomes idle or is reprogrammed

after a buffer transfer completes or is terminated.

The single data-transfer mode is compatible with all of the buffer-transfer modes. The following

flowcharts show the transfer process flow for a channel programmed for single data-transfer

mode with each buffer-transfer mode: single (Figure 12-8), autoinitialize (Figure 12-9), and

chaining (Figure 12-10).

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