CHAPTER 7 DMAC
Preliminary User’s Manual A14874EJ3V0UM
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7.8.3 Line transfer mode
In line transfer mode, the DMAC releases the bus after every four byte, halfword, or word transfers. If there is a
subsequent DMA transfer request, four transfers are performed again. This operation continues until a terminal count
occurs. In 2-cycle transfer, the operation from read to write is repeated four times.
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 line 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 7-18 to 7-21 show examples for line transfer.
Figure 7-18. Line Transfer Example 1
DMARQ3
(Input)
DMA3
DMA3
CPU
DMA3 DMA3 DMA3
CPU
CPU
DMA3
CPU
DMA3 DMA3 DMA3
DMA3
CPU
DMA3 DMA3
CPU
CPU
DMA channel 3
terminal count
Note
Note
Note
The bus is always released.
Figure 7-19 shows a line 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 line transfer.
Figure 7-19. Line Transfer Example 2
DMA1
DMA2
CPU
DMA2 CPU DMA3
DMA3
CPU
DMA0
DMA0
CPU DMA1
CPU
CPU
CPU
CPU
DMARQ3
(Input)
DMARQ2
(Input)
DMARQ1
(Input)
DMARQ0
(Input)
Note
Note
Note
Note
DMA3 DMA3
DMA channel 0
terminal count
DMA channel 2
terminal count
DMA channel 1
terminal count
DMA3 DMA3 DMA3
DMA3
Note
DMA channel 3
terminal count
Note
The bus is always released.