The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

BASICS OF COMPUTER SYSTEMS 0-51

If, say, a peripheral wants DMA service, it sends a request to the processor. The

DMA request is placed on the HOLD pin. Since DMA is a high priority issue, the

processor stops whatever it is doing and sends the acknowledge signal HLDA to the

peripheral. With this, the processor’s buses are tri stated such that the processor effec-

tively gets cut off from the system. Thus, a direct path of data transfer is established

between the peripheral and memory. Once this data transfer is over, the HOLD request

is removed by the peripheral and the processor gets back its status as the master of the

system.

0.9.4.7

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