Datasheet

Section 7 DMA Controller (DMAC)
Page 382 of 1408 R01UH0309EJ0500 Rev. 5.00
Sep 24, 2012
H8S/2456, H8S/2456R, H8S/2454 Group
(5) DREQ Pin Falling Edge Activation Timing
Set the DTA bit in DMABCRH to 1 for the channel for which the DREQ pin is selected.
Figure 7.22 shows an example of normal mode transfer activated by the DREQ pin falling edge.
DMA
read
Address
bus
φ
DREQ
Idle Write Idle
Bus release
DMA
control
Channel
Write Idle
Transfer source
Request
[1] [3][2] [4] [6][5] [7]
Acceptance resumes
Acceptance resumes
DMA
write
Bus
release
DMA
read
DMA
write
Bus
release
Request
Transfer destination Transfer source Transfer destination
Read Read
Request clear periodRequest clear period
Minimum
of 2 cycles
Minimum
of 2 cycles
[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 7.22 Example of DREQ Pin Falling Edge Activated Normal Mode Transfer