CHAPTER 6 DMA FUNCTIONS (DMA CONTROLLER)
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User’s Manual U14359EJ4V0UM
6.5
Transfer Modes
6.5.1 Single transfer mode
In single transfer mode, the DMAC releases the bus at each byte/halfword 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 takes precedence. If other DMA transfer request with the lower priority occurs one clock after single
transfer has been completed, however, this request does not take precedence even if the previous DMA transfer
request signal with the higher priority remains active. DMA transfer with the lower priority newly request is executed
after the CPU bus has been released.
Figures 6-2 to 6-5 show examples of single transfer.
Figure 6-2. Single Transfer Example 1
CPU
DMARQ3
(input)
CPU DMA3 CPU DMA3 CPU DMA3 CPU CPU CPU CPU CPU CPU DMA3 CPU DMA3 CPU CPU CPU
DMA channel 3 terminal count
Note
Note
Note
Note
Note
The bus is always released.
Figure 6-3 shows an example of a single transfer in which a higher priority DMA request is issued. DMA channels
0 to 2 are in the block transfer mode and channel 3 is in the single transfer mode.
Figure 6-3. Single Transfer Example 2
CPU CPU CPU DMA3 CPU DMA0 DMA0 CPU DMA1 DMA1 CPU DMA2 DMA2 CPU DMA3 CPU DMA3
DMARQ3
(input)
DMARQ2
(input)
DMARQ1
(input)
DMARQ0
(input)
DMA channel 3
terminal count
DMA channel 0
terminal count
DMA channel 2
terminal count
Note
Note
Note
Note
DMA channel 1
terminal count
Note
The bus is always released.