HD6417706 Datasheet, PDF (305/709 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer Super RISC engine Family/SH7700 Series

9.4.3 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 the priority bits PR1 and PR0 in the DMA operation register (DMAOR).
Fixed Mode: In this mode, the priority levels among the channels remain fixed. There are three
kinds of fixed modes as follows:
• CH0 > CH1 > CH2 > CH3
• CH0 > CH2 > CH3 > CH1
• CH2 > CH0 > CH1 > CH3
These are selected by the PR1 and the PR0 bits in the DMA operation register (DMAOR).
Round-Robin Mode: Each time one word, byte, or longword, or 16-byte data 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 9.3.
The priority of the round-robin mode is CH0 > CH1 > CH2 > CH3 immediately after a reset.
Rev. 4.00, 03/04, page 259 of 660