364
CPU
CPU
CPU
DMAC DMAC
CPU
DMAC DMAC CPU
CPU
DREQ
Bus cycle
Bus returned to CPU
Read
Write
Write
Read
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
DMAC
DMAC DMAC
CPU
DREQ
Bus cycle
Read
Read
Read
Write
Write
Write
Figure 11.13 Example of Transfer in Burst Mode
Содержание SH7709S
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Страница 292: ...273 T1 CKIO A25 to A0 CSn RD WR RD D31 to D0 WEn D31 to D0 BS T2 Read Write Figure 10 6 Basic Timing of Basic Interface ...
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