HD6432633 Datasheet, PDF (360/1453 Pages) Renesas Technology Corp – Series of Microcomputers (MCUs: microcomputer units)

DREQ Pin Falling Edge Activation Timing: Set the DTA bit for the channel for which the
DREQ pin is selected to 1.
Figure 8-23 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 8-23 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.
306