Z80 Datasheet, PDF (122/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

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End-of-Block Action
Bit 5 specifies either a stop (bus release) or an auto repeat at the end of the
block length programmed in WR0. To interrupt at the end of a block
(WR4), bit 5 should be 0 because the DMA must reset the end-of-block
status bit to proceed with a new block. In Auto Restart, the end-of-block
status bit is also reset.
CE/WAIT Line Use
Bit 4 specifies that the DMA’s CE/WAIT line is to be used in one of two
ways:
CE Only
The CE/WAIT line functions only as a chip enable line, allowing CPU
writing and reading of control/status bytes when the DMA is not bus
master. See the “Applications” chapter for the method by which this time is
decoded from the address bus.
CE/WAIT Multiplex
This line functions as described in “CE only” above, when the DMA is not
bus master. When the DMA has the bus, however, the line allows external
Wait inputs from external logic to extend the DMA's cycle programmed in
WR1 and/or WR2. See the “Applications” chapter for hardware interfacing
of this option.
Ready-Line State
Bit 3 specifies that the DMA interprets the Ready (RDY) line as active
when High or active when Low. This allows flexibility in interfacing to a
variety of other devices.
UM008101-0601
Direct Memory Access