Zilog Z08470 - Manual (Page 71)

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UM008101-0601 Direct Memory Access
Figure 22. Burst Mode
In the Burst mode (Figure 22), the bus is requested in the same manner as
previously, but when the DMA has control of the bus it continues to transfer
bytes until it encounters either an inactive Ready signal from an I/O port, an
end-of-block, or a byte match as in Figure 20. If the Ready line goes
inactive before end-of-block is reached, the DMA releases the bus to the
CPU and repetitively tests the Ready signal until it comes active again.
Then it requests the bus again and continues its transfers. Because of this,
the Burst mode is often the most useful one for general-purpose applica-
tions. It does not request the bus until it actually can use it, but once it
RDY
Active
?
• Interrupt
• Release Bus
• Auto Restart
Request Bus
Enable
DMA
End
?
of Block
NO
NO
YES
Set Status Flag
NO
Request Bus
RDY
Active
?
YES
YES
Transfer/Search One Byte
(See Figure 20)