Renesas H8S Series Hardware Manual page 257

DREQ Pin Low Level Activation Timing: Set the DTA bit for the channel for which the DREQ pin is selected to 1.
Figure 7-32 shows an example of DREQ pin low level activated single address mode transfer.
DREQ
Address bus
DACK
DMA control
Channel
Acceptance after transfer enabling; the DREQ pin low level is sampled on the rising
[1]
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] The DMAC cycle is started.
[4] [7] Acceptance is resumed after the single 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 7-32 Example of DREQ Pin Low Level Activated Single Address 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. 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.
Bus release
ø
Idle Single
Request
Minimum of
2 cycles
[1] [2] [3]
DMA single Bus release
Transfer source/
destination
Idle
Request clear
period Request
Minimum of
2 cycles
[4] [5]
Acceptance resumes
Bus
DMA single
release
Transfer source/
destination
Single Idle
Request clear
period
[6] [7]
Acceptance resumes
Rev.6.00 Oct.28.2004 page 229 of 1016
REJ09B0138-0600H