![](http://datasheet.mmic.net.cn/90000/M37641M8-XXXHP_datasheet_3496247/M37641M8-XXXHP_230.png)
Rev.2.00
Aug 28, 2006
page 99 of 148
7641 Group
REJ09B0336-0200
APPLICATION
2.5 DMAC
2.5.7 Notes on DMAC
(1) Transfer time
One-byte data transfer requires 2 cycles of
φ (read and write cycles).
To perform DMAC transfer due to the different transfer requests on the same DMAC channel or
DMAC transfer between both DMAC channels, 1 cycle of
φ or more is needed before transfer is
started.
(2) Priority
The DMAC places a higher priority on channel-0 transfer requests than on channel-1 transfer
requests.
If a channel-0 transfer request occurs during a channel-1 burst transfer operation, the DMAC
completes the next transfer source and destination read/write operation first, and then stops the
channel-1 transfer operation.
The channel-1 transfer operation which has been suspended is automatically resumed from the
point where it was suspended so that channel-1 transfer can complete its one-burst transfer unit.
This will be performed even if another channel-0 transfer request occurs.
The suspended transfer due to the interrupt can also be resumed during its interrupt process
routine by writing “1” to the DMAC channel x enable bit (DxCEN).
(3) Related registers
A read/write must be performed to the source registers, transfer destination registers and transfer
count registers as follows:
Read from each higher byte first, then the lower byte
Write to each lower byte first, then the higher byte.
Note that if the lower byte is read out first, the values are the higher byte’s.
Do not access the DMAC-related registers by using a DMAC transfer. The destination address
data and the source address data will collide in the DMAC internal bus.
When setting the DMAC channel x enable bit (bit 7 of address 4116) to “1”, be sure simultaneously
to set the DMAC channel x transfer initiation source capture register reset bit (bit 6 of address
4116) to “1”. If this is not performed, an incorrect data will be transferred at the same time when
the DMAC is enabled.
(4) USB transfer
One signal among USB endpoint signals 1 to 4 can be selected as the hardware transfer request
source. This can realize that transfer between the USB FIFO and the master CPU bus interface
input/output buffer is performed effectively. This transfer function is only valid in the cycle steal
transfer mode.
(5) DMAOUT pin
In the memory expansion mode and microprocessor mode, the DMAOUT pin (P33/DMAOUT) outputs
“H” during a DMA transfer.