HD6432351 datasheet(312/1025 Pages) RENESAS

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Section 7 DMA Controller (DMAC)

Rev. 3.00 Sep 15, 2006 page 278 of 988

REJ09B0330-0300

request is cleared. After the end of the single cycle, acceptance resumes,

DREQ pin low level

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

7.5.12

Write Data Buffer Function

DMAC internal-to-external dual address transfers and single address transfers can be executed at

high speed using the write data buffer function, enabling system throughput to be improved.

When the WDBE bit of BCRL in the bus controller is set to 1, enabling the write data buffer

function, dual address transfer external write cycles or single address transfers and internal

accesses (on-chip memory or internal I/O registers) are executed in parallel. Internal accesses are

independent of the bus master, and DMAC dead cycles are regarded as internal accesses.

A low level can always be output from the

TEND pin if the bus cycle in which a low level is to be

output is an external bus cycle. However, a low level is not output from the

TEND pin if the bus

cycle in which a low level is to be output from the

TEND pin is an internal bus cycle, and an

external write cycle is executed in parallel with this cycle.

Figure 7.33 shows an example of burst mode transfer from on-chip RAM to external memory

using the write data buffer function.

Internal address

Internal read signal

HWR, LWR

TEND

External address

DMA

read

DMA

write

DMA

read

DMA

write

DMA

read

DMA

write

DMA

read

DMA

write

DMA

dead

Figure 7.33 Example of Dual Address Transfer Using Write Data Buffer Function

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