CHAPTER 6 DMA FUNCTIONS (DMA CONTROLLER)
120
User’s Manual U15195EJ5V0UD
6.4 Transfer
Modes
6.4.1 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 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 6-1 to 6-4 show examples of single transfer.
Figure 6-1. Single Transfer Example 1
CPU
DMA3
CPU
CPU
DMA3
CPU
CPU
CPU
CPU
CPU
DMA3
CPU
DMA3
DMA3
CPU
CPU
CPU
DMARQ3
(Internal signal)
CPU
CPU
DMA channel 3 terminal count
Note
Note
Note
Note
Note
The bus is always released.
Figure 6-2 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 6-2. Single Transfer Example 2
DMA1
DMA2
CPU
DMA2
CPU DMA3
CPU
CPU
CPU
DMA3
CPU
DMA0
DMA0
CPU
DMA1
DMARQ3
CPU DMA3
DMARQ2
DMARQ1
DMARQ0
Note
Note
Note
Note
DMA channel 0
terminal count
DMA channel 2
terminal count
DMA channel 3
terminal count
DMA channel 1
terminal count
(Internal signal)
(Internal signal)
(Internal signal)
(Internal signal)
Note
The bus is always released.
Содержание PD703114
Страница 2: ...2 User s Manual U15195EJ5V0UD MEMO ...