SH7720 Datasheet, PDF (493/1524 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 10 Direct Memory Access Controller (DMAC)
10.4.3 Channel Priority
When the DMAC receives simultaneous transfer requests on two or more channels, it transfers
data according to a predetermined priority. Two modes (fixed mode and round-robin mode) are
selected by the PR1 and PR0 bits in DMAOR.
(1) Fixed Mode
In this mode, the priority levels among the channels remain fixed. There are two kinds of fixed
modes as follows:
• CH0 > CH1 > CH2 > CH3 > CH4 > CH5
• CH0 > CH2 > CH3 > CH1 > CH4 > CH5
These are selected by the PR1 and the PR0 bits in DMAOR.
(2) Round-Robin Mode
In round-robin mode each time data of one transfer unit (word, byte, longword, or 16-byte unit) is
transferred on one channel, the priority is rotated. The channel on which the transfer was just
finished rotates to the bottom of the priority. The round-robin mode operation is shown in figure
10.3. The priority of round-robin mode is CH0 > CH1 > CH2 > CH3 > CH4 > CH5 immediately
after a reset. When round-robin mode is specified, the same bus mode, either cycle steal mode or
burst mode, must be specified for all of the channels.
Rev. 3.00 Jan. 18, 2008 Page 431 of 1458
REJ09B0033-0300