3069RF-ZTAT Datasheet, PDF (263/1003 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER

7.4.9 Multiple-Channel Operation
The DMAC channel priority order is: channel 0 > channel 1 and channel A > channel B.
Table 7.12 shows the complete priority order.
Table 7.12 Channel Priority Order
Short Address Mode
Channel 0A
Channel 0B
Channel 1A
Channel 1B
Full Address Mode
Channel 0
Channel 1
Priority
High
Low
If transfers are requested on two or more channels simultaneously, or if a transfer on one channel
is requested during a transfer on another channel, the DMAC operates as follows.
• When a transfer is requested, the DMAC requests the bus right. When it gets the bus right, it
starts a transfer on the highest-priority channel at that time.
• Once a transfer starts on one channel, requests to other channels are held pending until that
channel releases the bus.
• After each transfer in short address mode, and each externally-requested or cycle-steal transfer
in normal mode, the DMAC releases the bus and returns to step 1. After releasing the bus, if
there is a transfer request for another channel, the DMAC requests the bus again.
• After completion of a burst-mode transfer, or after transfer of one block in block transfer
mode, the DMAC releases the bus and returns to step 1. If there is a transfer request for a
higher-priority channel or a bus request from a higher-priority bus master, however, the
DMAC releases the bus after completing the transfer of the current byte or word. After
releasing the bus, if there is a transfer request for another channel, the DMAC requests the bus
again.
Figure 7.19 shows the timing when channel 0A is set up for I/O mode and channel 1 for burst
mode, and a transfer request for channel 0A is received while channel 1 is active.
Rev. 5.0, 09/04, page 241 of 978