Renesas SH7709S Manual De Usuario
Rev. 5.00, 09/03, page 349 of 760
11.3.3
Channel Priority
When the DMAC receives simultaneous transfer requests on two or more channels, it selects a
channel according to a predetermined priority order. Two modes (fixed mode and round-robin
mode) are selected by priority bits PR1 and PR0 in the DMA operation register (DMAOR).
channel according to a predetermined priority order. Two modes (fixed mode and round-robin
mode) are selected by priority bits PR1 and PR0 in the DMA operation register (DMAOR).
Fixed Mode: In these modes, the priority order of the channels remain fixed. There are three kinds
of fixed modes as follows:
of fixed modes as follows:
CH0 > CH1 > CH2 > CH3
CH0 > CH2 > CH3 > CH1
CH2 > CH0 > CH1 > CH3
CH0 > CH2 > CH3 > CH1
CH2 > CH0 > CH1 > CH3
These are selected by the PR1 and PR0 bits in DMAOR.
Round-Robin Mode: Each time one word, byte, or longword is transferred on one channel, the
priority order is rotated. The channel on which the transfer was just finished rotates to the bottom
of the priority order. The round-robin mode operation is shown in figure 11.3. The priority of the
round-robin mode is CH0 > CH1 > CH2 > CH3 immediately after reset.
priority order is rotated. The channel on which the transfer was just finished rotates to the bottom
of the priority order. The round-robin mode operation is shown in figure 11.3. The priority of the
round-robin mode is CH0 > CH1 > CH2 > CH3 immediately after reset.