H8SSLASH2214 datasheet(291/936 Pages) RENESAS

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Section 7 DMA Controller

Rev.4.00 Sep. 18, 2008 Page 231 of 872

REJ09B0189-0400

channel is activated first. Transfer requests for other channels are held pending in the DMAC, and

activation is carried out in order of priority.

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.

(2) 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.

(3) 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.

H8S/2214 Scheda tecnica(PDF) 291 Page - Renesas Technology Corp