r4f2426 Renesas Electronics Corporation., r4f2426 Datasheet - Page 399

• Manufacturer Part Number: r4f2426
• Description: 16-bit Single-chip Microcomputer H8s Family / H8s/2400 Series
• Manufacturer: Renesas Electronics Corporation.

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.
φ
DREQ
Address
bus
DMA
control
Channel
[1]
[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
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
Acceptance after transfer enabling; the DREQ pin low level is sampled on the rising edge of φ,
and the request is held.
is completed.
(As in [1], the DREQ pin low level is sampled on the rising edge of φ, and the request is held.)
Bus release
Idle
[1]
Request
of 2 cycles
Minimum
[2]
Request clear period
Read
[3]
Transfer source
DMA
read
Write
1 block transfer
Acceptance resumes
Transfer destination
DMA
write
Dead
[4]
Request
DMA
dead
of 2 cycles
Minimum
Idle
[5]
release
Bus
Read
[6]
Rev. 1.00 Sep. 19, 2008 Page 371 of 1270
Transfer source
Request clear period
DMA
read
Write
Section 7 DMA Controller (DMAC)
1 block transfer
Transfer destination
DMA
write
Dead
Acceptance resumes
REJ09B0466-0100
DMA
dead
[7]
Idle
release
Bus