H8SSLASH2218 datasheet(249/750 Pages) RENESAS

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Section 7 DMA Controller (DMAC)

Rev.6.00 Jun. 03, 2008 Page 201 of 698

REJ09B0074-0600

DREQ Signal Level Activation Timing (Normal Mode): Set the DTA bit for the channel for

which the

DREQ signal is selected to 1.

Figure 7.19 shows an example of

DREQ level activated normal mode transfer.

DREQ

Bus release

Idle

Read

Request clear period

Acceptance resumes

Minimum of 2 cycles

Request clear period

Request

Transfer

source

Transfer

source

Transfer

destination

Transfer

destination

Read

Write

Address bus

DMA control

Channel

DMA

read

DMA

write

Bus

release

DMA

read

DMA

write

Bus

release

[1]

[2]

[3]

[4]

[5]

[6]

[7]

Acceptance after transfer enabling; the

DREQ signal low level is sampled on the rising

edge of f, 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.

Acceptance is resumed after the write cycle is completed.

(As in [1], the

DREQ signal low level is sampled on the rising edge of φ, and the request

is held.)

[1]

[2] [5]

[3] [6]

[4] [7]

Figure 7.19 Example of

DREQ Level Activated Normal Mode Transfer

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

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

request is cleared. Acceptance resumes after the end of the write cycle,

DREQ signal low level

sampling is performed again, and this operation is repeated until the transfer ends.

Note: The

DREQ signal of this chip is an internal signal of chip, so it is not output from the pin.

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