190
Chapter 7
DMA Functions (DMA Controller)
Preliminary User’s Manual U15839EE1V0UM00
7.5.3 Line Transfer Mode
In line transfer mode, the DMAC releases the bus after every four byte, halfword or word transfer. If
there is a subsequent DMA transfer request, four transfers are performed again. This operation contin-
ues until a terminal count occurs. In two-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.
Figure 7-22, “Line Transfer Example 1,” on page 190 shows a DMA transfer example in line transfer
mode.
Figure 7-22:
Line Transfer Example 1
Figure 7-23, “Line Transfer Example 2,” on page 190 shows DMAC transfers in line transfer mode 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 7-23:
Line Transfer Example 2
Note: The bus is always released
DMA3
DMA3
CPU
DMA3 DMA3 DMA3
CPU
CPU
DMA3
CPU
DMA3 DMA3 DMA3
DMA3
CPU
DMA3 DMA3
CPU
CPU
Note
Note
DMA Transfer
Request CH3
DMA channel 3
terminal count
DMA Transfer
Request CH0
DMA Transfer
Request CH1
DMA Transfer
Request CH2
DMA channel 0
terminal count
DMA channel 1
terminal count
DMA channel 2
terminal count
DMA1
DMA2
CPU
DMA2
CPU DMA3
DMA3
CPU
DMA0
DMA0
CPU
DMA1
CPU
CPU
CPU
CPU
Note
Note
Note
Note
DMA3 DMA3
DMA3 DMA3 DMA3
DMA3
Note
DMA Transfer
Request CH3
DMA channel 3
terminal count
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