H8SSLASH2214 datasheet(297/936 Pages) RENESAS

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Section 7 DMA Controller

Rev.4.00 Sep. 18, 2008 Page 237 of 872

REJ09B0189-0400

(5)

DREQ Pin Falling Edge Activation Timing

Set the DTA bit for the channel for which the

DREQ pin is selected to 1.

Figure 7.20 shows an example of

DREQ pin falling edge activated normal 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

write 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

Idle

Bus release

DMA control

Channel

Write

Idle

Transfer

source

Request

Minimum of 2 cycles

[1]

[3]

[2]

[4]

[6]

[5]

[7]

Acceptance resumes

DMA

write

Bus

release

DMA

read

DMA

write

Bus

release

Request

Minimum of 2 cycles

Transfer

destination

Transfer

source

Transfer

destination

Request clear period

Read

Figure 7.20 Example of

DREQ Pin Falling Edge Activated Normal 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 write cycle ends, acceptance

resumes after the end of the write cycle,

DREQ pin low level sampling is performed again, and

this operation is repeated until the transfer ends.

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