H8SSLASH2214 datasheet(298/936 Pages) RENESAS

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Section 7 DMA Controller

Rev.4.00 Sep. 18, 2008 Page 238 of 872

REJ09B0189-0400

Figure 7.21 shows an example of

DREQ pin falling edge activated block transfer mode transfer.

[1]

[2] [5]

[3] [6]

[4] [7]

Note: In write data buffer mode, bus breaks from [2] to [7] may be hidden, and not visible.

Acceptance after transfer enabling; the

DREQ pin low level is sampled on the rising edge of φ,

and the request is held.

The request is cleared at the next bus break, and activation is started in the DMAC.

Start of DMA cycle;

DREQ pin high level sampling on the rising edge of φ starts.

When the

DREQ pin high level has been sampled, acceptance is resumed after the dead cycle

is completed.

(As in [1], the

DREQ pin low level is sampled on the rising edge of φ, and the request is held.)

DMA

read

Address bus

DREQ

Idle

Write

Bus release

DMA control

Channel

Write

Transfer

source

Request

Minimun of 2 cycles

[1]

[3]

[2]

[4]

[6]

[5]

[7]

Acceptance resumes

DMA

dead

1 block transfer

Idle

Dead

DMA

write

Bus

release

DMA

read

DMA

write

DMA

dead

Bus

release

Transfer

source

Transfer

destination

Request clear period

Minimun of 2 cycles

Request

Acceptance resumes

1 block transfer

Request clear period

Read

Transfer

destination

Idle

Figure 7.21 Example of

DREQ Pin Falling Edge Activated Block Transfer Mode Transfer

DREQ pin sampling is performed every cycle, with the rising edge of the next φ cycle after the

end of the DMABCR write cycle for setting the transfer enabled state as the starting point.

When the

DREQ pin low level is sampled while acceptance by means of the DREQ pin is

possible, the request is held in the DMAC. Then, when activation is initiated in the DMAC, the

request is cleared, and

DREQ pin high level sampling for edge detection is started. If DREQ pin

high level sampling has been completed by the time the DMA dead cycle ends, acceptance

resumes after the end of the dead cycle,

DREQ pin low level sampling is performed again, and this

operation is repeated until the transfer ends.

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