Z80 Datasheet, PDF (67/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

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Memory
DMA
I/O
1. Transfer Memory-to-I/O (optional search)
2. Transfer I/O-to-Memory (optional search)
1
3. Transfer Memory-to-Memory (optional search)
4. Transfer I/O-to-I/O (optional search)
2
5. Search Memory
6. Search I/O
3
4
5
I/O
6
Figure 19. Basic Functions of the Z80 DMA
Modes of Operation
Within any class of operation, the Z80 DMA can be programmed to operate
in one of three Transfer and/or, Search modes:
Byte Mode
Data operations are performed one byte at a time. Between each byte oper-
ation the system bus is released to the CPU. The bus is requested again for
each succeeding byte operation. This is also sometimes called Single mode
or byte-at-a-time mode.
Burst Mode
Data operations continue until a port’s Ready line to the DMA goes
inactive. The DMA then stops (releases the system bus) after completing its
current byte operation. This is also called demand mode.
Continuous Mode
Data operations continue until the end of the programmed block of data or a
stop-on-match condition is reached before the system bus is released. If a
UM008101-0601
Direct Memory Access