328
Chapter 8
DMA Controller (DMAC)
Preliminary User’s Manual U17566EE1V2UM00
8.12 Transfer Mode
8.12.1
Single transfer mode
In single transfer mode, the DMAC releases the bus after each byte/halfword/
word transfer. If there is a subsequent DMA transfer request, transfer is
performed again once. This operation continues until a terminal count occurs.
When the DMAC has released the bus, if another higher priority DMA transfer
request is issued, the higher priority DMA request always takes precedence.
However, if a lower priority DMA transfer request is generated within one clock
after the end of a single transfer, even if the previous higher priority DMA
transfer request signal stays active, this request is not prioritized and the next
DMA transfer after the bus is released for the CPU is a transfer based on the
newly generated, lower priority DMA transfer request.
Figure 8-5
shows a DMAC transfer in single transfer mode. In this example the
DMA channel 3 is used for a single transfer.
Figure 8-5
Single transfer example 1
Note
The bus is always released
CPU
DMA3
CPU
CPU
DMA3
CPU
CPU
CPU
CPU
CPU
DMA3
CPU
DMA3
DMA3
CPU
CPU
CPU
CPU
CPU
DMA chan nel 3 terminal count
Note
Note
Note
Note
DMA Transfer
Request CH3
electronic components distributor