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TC1784
Direct Memory Access Controller (DMA)
User´s Manual
11-8
V1.1, 2011-05
DMA, V3.03
When writing a new address to the (address of) the source or destination address
register and no DMA transaction is running, the new address value is directly written into
the source or destination address register. In this case, no buffering of the address is
required. When writing a new address to the (address of) the source or destination
address register and a DMA transaction is running, no transfer to an address register can
take place and SHADRmn holds the new address value that was written. For this
operation, bit field ADRCRmn.SHCT must be set either to 01
B
(address is a source
address) or 10
B
(new address is a destination address). At the start of the next DMA
transaction, the shadow transfer takes place and the content of SHADRmn is written
either into SADRmn or DADRmn (ADRCRmn.SHCT must be set accordingly). After the
shadow transfer, SHADRmn is set to 0000 0000
H
if the shadow register write enable bit
is set to 0 (ADRCRmn.SHWEN = 0). In this case (ADRCRmn.SHWEN = 0), the software
can check by reading the shadow address register whether or not the shadow transfer
has already taken place.
Only one address register can be shadowed while a transaction is running, because the
shadow register can only be assigned either to the source or to the destination address
register. Note that the shadow address register transfer has the same behavior in Single
and Continuous Mode. When the shadow mechanism is disabled
(ADRCRmn.SHCT = 00
B
), SHADRmn is always read as 0000 0000
H
.
If the shadow address register write enable bit is set to 1 (ADRCRmn.SHWEN = 1), the
shadow register SHADRmn can be directly written. In this case
(ADRCRmn.SHWEN = 1) the value stored in the SHADRmn is not modified when the
shadow transfer takes place, and the shadow mechanism remains active and the
shadow transfer will be repeated until Channel mn is reset or until the value in SHADR
is 0000 0000
H
, is written into the shadow register (direct or indirect by writing to the
source or destination address register according to the shadow control register
ADRCRmn.SHCT).
Содержание TC1784
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