Rev. 2.00, 09/03, page 265 of 690
Figure 8.10 shows an example of DMA transfer timing in cycle steal intermittent mode.
Transfer conditions shown in the figure are:
Dual address mode
DREQ low level detection
DREQ
CPU
CPU
Bus cycle
CPU
More than 16 or 64 B
φ
(change by the CPU's condition of using bus)
DMAC DMAC
CPU
CPU
DMAC DMAC
CPU
Read/Write
Read/Write
Figure 8.10 Example of DMA Transfer in Cycle Steal Intermittent Mode
(Dual Address, DREQ Low Level Detection)
b. Burst Mode
Once the bus right is obtained, the transfer is performed continuously until the transfer end
condition is satisfied. In external request mode with low level detection of the DREQ pin,
however, when the DREQ pin is driven high, the bus passes to the other bus master after the
DMAC transfer request that has already been accepted ends, even if the transfer end conditions
have not been satisfied.
Burst mode cannot be used for other than the CMT when the on-chip peripheral module is the
transfer request source. Figure 8.11 shows DMA transfer timing in burst mode.
CPU
CPU
CPU
DMAC DMAC DMAC
DMAC
DMAC DMAC
CPU
DREQ
Bus cycle
Read
Read
Read
Write
Write
Write
Figure 8.11 DMA Transfer Example in Burst Mode
(Dual Address, DREQ Low Level Detection)
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