D12320VF25IV Datasheet, PDF (319/1304 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 7 DMA Controller (Not Supported in the H8S/2321)
DREQ Pin Falling Edge Activation Timing: Set the DTA bit for the channel for which the
DREQ pin is selected to 1.
Figure 7.23 shows an example of DREQ pin falling edge activated normal mode transfer.
Bus release
DMA
read
DMA
write
Bus
release
DMA
read
DMA
write
Bus
release
φ
DREQ
Address
bus
DMA
control ^Idle
Transfer source Transfer destination
Read Write
Idle
Transfer source Transfer destination
Read Write
Idle
Channel
Request
Minimum
of 2 cycles
Request clear period
Request
Minimum
of 2 cycles
Request clear period
[1] [2] [3]
[4] [5] [6]
[7]
Acceptance resumes
Acceptance resumes
[1] Acceptance after transfer enabling; the DREQ pin low level is sampled on the rising edge of φ,
and the request is held.
[2] [5] The request is cleared at the next bus break, and activation is started in the DMAC.
[3] [6] Start of DMA cycle; DREQ pin high level sampling on the rising edge of φ starts.
[4] [7] 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.)
Note: In write data buffer mode, bus breaks from [2] to [7] may be hidden, and not visible.
Figure 7.23 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.
Rev.6.00 Sep. 27, 2007 Page 287 of 1268
REJ09B0220-0600