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Rev. 5.00, 09/03, page 360 of 760
CPU CPU CPU DMAC DMAC CPU DMAC DMAC CPU CPU
DREQ
Bus cycle
Bus returned to CPU
Read Write WriteRead
Figure 11.12 Example of DMA Transfer in Cycle-Steal Mode
• Burst Mode
Once the bus 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 when a serial communication interface (IrDA, SCI), or A/D
converter is the transfer request source. Figure 11.13 shows an example of burst mode timing.
CPU CPU CPU DMAC DMAC DMAC DMACDMAC DMAC CPU
DREQ
Bus cycle
Read Read ReadWrite Write Write
Figure 11.13 Example of Transfer in Burst Mode