Explain the various modes in which DMAC works.
Working of Direct memory access controller:
The modes of operation has demand mode, block mode, single mode and cascade mode. Demand mode transfers data till an external EOP is input or till the DREQ input becomes inactive. Particular mode releases the HOLD after all byte of data transferred. Block mode automatically transfers the no. of bytes specified by the county register for the channel. Cascade mode is used while more than one 8237 is present into a system.