CHAPTER 7 DMAC
Preliminary User’s Manual A14874EJ3V0UM
166
7.8 Transfer Modes
7.8.1 Single transfer mode
In single transfer mode, the DMAC releases the bus after each byte, halfword, or word transfer. If there is a
subsequent DMA transfer request, a single transfer is performed again. This operation continues until a terminal
count occurs.
If a higher priority DMA transfer request is generated while the DMAC has released the bus, the higher priority
DMA transfer 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.
Figures 7-12 to 7-15 show examples for single transfer.
Figure 7-12. Single Transfer Example 1
CPU
DMA3
CPU
CPU DMA3 CPU
CPU
CPU
CPU
CPU
DMA3 CPU DMA3
DMA3
CPU
CPU
CPU
DMARQ3
(Input)
CPU
CPU
DMA channel 3 terminal count
Note
Note
Note
Note
Note
The bus is always released.
Figure 7-13 shows a single transfer mode example in which a higher priority DMA transfer request is generated.
DMA channels 0 to 2 are used for a block transfer, and channel 3 is used for a single transfer.
Figure 7-13. Single Transfer Example 2
DMA1
DMA2
CPU
DMA2 CPU DMA3
CPU
CPU
CPU DMA3
CPU
DMA0
DMA0
CPU DMA1
DMARQ3
(Input)
CPU DMA3
DMARQ2
(Input)
DMARQ1
(Input)
DMARQ0
(Input)
Note
Note
Note
Note
DMA channel 0
terminal count
DMA channel 2
terminal count
DMA channel 3
terminal count
DMA channel 1
terminal count
Note
The bus is always released.