Z80 Datasheet, PDF (118/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

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DMA Enable
A1 in bit 6 of the base register enables the DMA to request the bus. This
function duplicates the ENABLE DMA command in WR6 and is used as
the last control byte written to the DMA prior to allowing the DMA to
usurp the bus from the CPU. The ENABLE DMA command is often better
for this purpose.
D7 D6 D5 D4 D3 D2 D1 D0
0
0 0 Base Register Byte
DMA Enable = 1
Interrupt Enable = 1
1 = Stop on Match
Mask Byte (0 = Compare)
Match Byte
Figure 43. Write Register 3 Group
Write Register 4 Group
Bits 7, 1, and 0, which Figure 44 shows, select the base register byte for this
group. The group specifies the following characteristics:
Operating Mode
Bits 6 and 5 of the base register specify the operating mode as Byte, Burst,
or Continuous. For a review of these modes, see Figure 41 through
Figure 44, Table 13 and Table 15.
UM008101-0601
Direct Memory Access