Datasheet

Section 7 DMA Controller (DMAC)
Page 384 of 1408 R01UH0309EJ0500 Rev. 5.00
Sep 24, 2012
H8S/2456, H8S/2456R, H8S/2454 Group
Figure 7.23 shows an example of block transfer mode transfer activated by the DREQ pin falling
edge.
DMA
read
A
ddress
bus
φ
DREQ
Idle Write
Bus release
DMA
control
Channel
Write
Transfer source
Request
[1] [3][2] [4] [6][5] [7]
Acceptance resumes
DMA
dead
1 block transfer
IdleDead Dead
DMA
write
Bus
release
DMA
read
DMA
write
DMA
dead
Bus
release
Transfer source
Request
Acceptance resumes
1 block transfer
Transfer destinationTransfer destination
ReadIdleRead
Minimum
of 2 cycles
Minimum
of 2 cycles
Request clear periodRequest clear period
[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 dead 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 Block Transfer 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 dead cycle ends, acceptance
resumes after the end of the dead cycle, DREQ pin low level sampling is performed again, and this
operation is repeated until the transfer ends.