DMA Hardware (8237 DMAC) :

1)Processor contain HOLD/HOLD Acknowledge lines to interact with 8237

o   DMAC can achieve control of ISA bus by asserting HOLD

o   Processor acknowledges with HLDA

2)DRQ4 services slave controller Priorities are set as fixed

o   DRQ0 highest and DRQ7 lowest

o   It set at POST

o   It can be reprogrammed for rotating priority

3)ISA address/data/control  lines are also linked (not shown)

o   It can access control registers through ports

o   Each channel has a page register associated with