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When DTE = 0, such as after completion of a transfer, a request from the selected activation
source is not sent to the DMAC, regardless of the DTA bit. In this case, the relevant interrupt
request is sent to the CPU or DTC.
In case of overlap with a CPU interrupt source or DTC activation source (DTA = 0), the interrupt
request flag is not cleared by the DMAC.
Activation by External Request: If an external request (
DREQ pin) is specified as an activation
source, the relevant port should be set to input mode in advance.
Level sensing or edge sensing can be used for external requests.
External request operation in normal mode (short address mode or full address mode) is described
below.
When edge sensing is selected, a 1-byte or 1-word transfer is executed each time a high-to-low
transition is detected on the
DREQ pin. The next transfer may not be performed if the next edge is
input before transfer is completed.
When level sensing is selected, the DMAC stands by for a transfer request while the
DREQ pin is
held high. While the
DREQ pin is held low, transfers continue in succession, with the bus being
released each time a byte or word is transferred. If the
DREQ pin goes high in the middle of a
transfer, the transfer is interrupted and the DMAC stands by for a transfer request.
Activation by Auto-Request: Auto-request activation is performed by register setting only, and
transfer continues to the end.
With auto-request activation, cycle steal mode or burst mode can be selected.
In cycle steal mode, the DMAC releases the bus to another bus master each time a byte or word is
transferred. DMA and CPU cycles usually alternate.
In burst mode, the DMAC keeps possession of the bus until the end of the transfer, and transfer is
performed continuously.