CHAPTER 6 DMA FUNCTIONS (DMA CONTROLLER)
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User’s Manual U14492EJ3V0UD
6.5.2 Single-step transfer mode
In single-step transfer mode, the DMAC releases the bus at each byte/halfword transfer. Once a DMA transfer
request signal is received, transfer is performed again. 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.
Figures 6-6 and 6-7 show examples of single-step transfer. Figure 6-7 shows a single-step transfer mode example
in which a higher priority DMA transfer request is generated. DMA channels 0 and 1 are used for the single-step
transfer.
Figure 6-6. Single-Step Transfer Example 1
DMA1
CPU
CPU
CPU
CPU
CPU
CPU
CPU
CPU
DMA1
CPU
CPU
DMA1
DMA1
CPU
DMARQ1
CPU
CPU
DMA channel 1
terminal count
Note
Note
Note
(Internal signal)
Note
The bus is always released.
Figure 6-7. Single-Step Transfer Example 2
DMA0
DMA0
CPU
CPU
DMA1 CPU
CPU
CPU
CPU
DMA1
CPU
CPU
DMA1
DMA0
CPU
DMARQ1
DMA1 CPU
DMARQ0
DMA channel 0
terminal count
DMA channel 1
terminal count
Note
Note
Note
Note
Note
Note
(Internal signal)
(Internal signal)
Note
The bus is always released.
6.5.3 Block transfer mode
In the block transfer mode, once transfer starts, the DMAC continues the transfer operation without releasing the
bus until a terminal count occurs. No other DMA requests are acknowledged during block transfer.
After the block transfer ends and the DMAC releases the bus, another DMA transfer can be acknowledged.
Содержание V850E/IA1 mPD703116
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