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MAR specifies the start address of the transfer source or transfer destination as 24 bits. MAR is
incremented or decremented by 1 or 2 each time a byte or word is transferred.
IOAR specifies the lower 16 bits of the other address. The 8 bits above IOAR have a value of
H'FF.
The number of transfers is specified as 8 bits by ETCRH and ETCRL. The maximum number of
transfers, when H'00 is set in both ETCRH and ETCRL, is 256.
In repeat mode, ETCRL functions as the transfer counter, and ETCRH is used to hold the number
of transfers. ETCRL is decremented by 1 each time a transfer is executed, and when its value
reaches H'00, it is loaded with the value in ETCRH. At the same time, the value set in MAR is
restored in accordance with the values of the DTSZ and DTID bits in DMACR. The MAR
restoration operation is as shown below.
DTID
DTSZ
MAR = MAR – (–1)
· 2
· ETCRH
The same value should be set in ETCRH and ETCRL.
In repeat mode, operation continues until the DTE bit is cleared. To end the transfer operation,
therefore, you should clear the DTE bit to 0. A transfer end interrupt request is not sent to the CPU
or DTC.
By setting the DTE bit to 1 again after it has been cleared, the operation can be restarted from the
transfer after that terminated when the DTE bit was cleared.
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