HD64F2357VF13 Datasheet, PDF (252/1049 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

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
ø
DREQ
Address bus
Transfer
source
Transfer
destination
Transfer
source
Transfer
destination
DMA control Idle
Read Write
Idle
Read Write
Idle
Channel
Request
Request clear period _Request
Request clear period
Minimum of 2 cycles
Minimum of 2 cycles
[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 ø, 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 ø 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 ø, 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 ø 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 Oct.28.2004 page 222 of 1016
REJ09B0138-0600H