CHAPTER 6 DMA FUNCTIONS (DMA CONTROLLER)
226
User’s Manual U14359EJ4V0UM
6.5.2 Single-step transfer mode
In single-step transfer mode, the DMAC releases the bus at each byte/halfword transfer. If there is a subsequent
DMA transfer request signal (DMARQ0 to DMARQ3), 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.
The following shows an example of a single-step transfer. Figure 6-7 shows an example of single-step transfer
made in which a higher priority DMA request is issued. DMA channels 0 and 1 are in the single-step transfer mode.
Figure 6-6. 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
(input)
Note
Note
Note
Note
The bus is always released.
Figure 6-7. 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
(input)
DMARQ0
(input)
Note
Note
Note
Note
Note
Note
Note
The bus is always released.