284
If transfer requests are issued simultaneously for more than one channel, or if a transfer request for
another channel is issued during a transfer, when the bus is released the DMAC selects the
highest-priority channel from among those issuing a request according to the priority order shown
in table 8-13.
During burst transfer, or when one block is being transferred in block transfer, the channel will not
be changed until the end of the transfer.
Figure 8-35 shows a transfer example in which transfer requests are issued simultaneously for
channels 0A, 0B, and 1.
DMA read
DMA write
DMA read
DMA write
DMA read
DMA write
DMA
read
ø
Address bus
RD
HWR
LWR
DMA control
Channel 0A
Channel 0B
Channel 1
Idle
Write
Idle
Read
Write
Idle
Read
Write
Read
Request clear
Request
hold
Request
hold
Request clear
Request clear
Bus
release
Channel 0A
transfer
Bus
release
Channel 0B
transfer
Channel 1 transfer
Bus
release
Request
hold
Read
Selection
Non-
selection
Selection
Figure 8-35 Example of Multi-Channel Transfer