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CHAPTER 15 DMAC
15.5 Descriptor Register in RAM
This descriptor register has the setup information for the corresponding channel in
DMA transfer mode.
The descriptor register has a 12-byte area for each channel that is allocated to the
memory address specified by DPDP.
See Table 15.2-1, " Channel descriptor addresses," for the first address of the
descriptor for each channel.
■
First Word of a Descriptor
The structure of the first word of a descriptor is shown below.
[bits 31 to 16] DMACT: Transfer count
These bits specify the number of times DMA transfer is to be performed. When 0000H is
specified, DMA transfer is performed 65,536 times.
The value is decremented by 1 each time DMA transfer is performed.
[bits 15 to 12] Reserved
[bits 11 to 8] BLK: Block size specification
These bits specify the size of blocks to be transferred in single/block transfer mode.
When 0 is specified, a block size of 16 is assumed.
Specify 1 for single transfer.
[bits 7, 6] SCS1, SCS0: Transfer source address update mode
31 16
R/W
15 14 13 12 11 10 9 8
R/W
7654 3210
R/W R/W R/W R/W R/W R/W R/W R/W
DMACT
DCS0DCS1SCS0SCS1 WS0 MOD1WS1
BLK
MOD0
Initial value: undefined