CHAPTER 6 DMA FUNCTIONS (DMA CONTROLLER)
User’s Manual U12688EJ4V0UM00
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6.5.2 Single-step transfer mode
In single-step transfer mode, DMAC releases the bus at each byte/halfword transfer. Once a request signal
(DMARQ0 to DMARQ3) is received, 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 6-4 and 6-5 show examples of single-step transfer.
Figure 6-4. Single-Step Transfer Example 1
CPU CPU CPU DMA1 CPU DMA1 CPU DMA1 CPU DMA1 CPU CPU CPU CPU CPU CPU CPU
DMA channel 1 terminal count
DMARQ1
Figure 6-5. Single-Step Transfer Example 2
CPU CPU CPU DMA1 CPU DMA1 CPU DMA0 CPU DMA0 CPU DMA0 CPU DMA1 CPU DMA1 CPU
DMA channel 0
terminal count
DMA channel 1
terminal count
DMARQ1
DMARQ0
6.5.3 Block transfer mode
In block transfer mode, once transfer starts, the transfer continues without the bus being released, until a terminal
count occurs. No other DMA requests are accepted during block transfer.
After the block transfer ends and DMAC releases the bus, another DMA transfer can be accepted.
Figures 6-6 shows an example of block transfer. In this block transfer example, a high priority DMA request is
issued. DMA channels 2 and 3 are in block transfer mode.
Note that caution is required when in block transfer mode. For details, refer to 6.19 Precautions.
Figure 6-6. Block Transfer Example
CPU CPU CPU DMA3
DMA3
DMA3
DMA3
DMA3
DMA3
DMA3
DMA3 CPU DMA2
DMA2
DMA2
DMA2
DMA2
DMA channel 3
terminal count
The bus is always released.
DMARQ3
DMARQ2
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