Datasheet

Section 8 DMA Controller (DMAC)
(This function is not available in the H8S/2695)
Page 318 of 1434 R01UH0166EJ0600 Rev. 6.00
Mar 02, 2011
H8S/2633 Group, H8S/2633 F-ZTAT
TM
,
H8S/2633R F-ZTAT
TM
, H8S/2695
Figure 8.24 shows an example of DREQ pin falling edge activated block transfer mode transfer.
[1]
[2] [5]
[3] [6]
[4] [7]
Note: In write data buffer mode, bus breaks from [2] to [7] may be hidden, and not visible.
Acceptance after transfer enabling; the DREQ pin low level is sampled on the rising edge of φ,
and the request is held.
The request is cleared at the next bus break, and activation is started in the DMAC.
Start of DMA cycle; DREQ pin high level sampling on the rising edge of φ starts.
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.)
DMA
read
φ
Address bus
DREQ
Idle Write
Bus release
DMA control
Channel
Write
Transfer
source
Request
Minimun of 2 cycles
[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
Transfer
destination
Request clear period
Minimun of 2 cycles
Request
Acceptance resumes
1 block transfer
Request clear period
ReadRead
Transfer
destination
Idle
Figure 8.24 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.