Rev.6.00 Oct.28.2004 page 228
of 1016
REJ09B0138-0600H
In the transfer end cycle (the cycle in which the transfer counter reaches 0), a one-state DMA dead cycle is inserted after
the DMA write cycle.
DREQ
Pin Falling Edge Activation Timing: Set the DTA bit for the channel for which the
DREQ
pin is selected to 1.
Figure 7-31 shows an example of
DREQ
pin falling edge activated single address mode transfer.
ø
DREQ
Bus release
DMA single
DMA single
Address bus
DMA control
Channel
[2]
DACK
Transfer source/
destination
Idle
Idle
Idle
Single
Single
[1]
[3]
[5]
[4]
[6]
[7]
Acceptance resumes
Acceptance resumes
Bus release
Bus release
Transfer source/
destination
Request
Request
Minimum of
2 cycles
Minimum of
2 cycles
Request clear
period
Request clear
period
[1]
[2] [5]
[3] [6]
[4] [7]
Acceptance after transfer enabling; the
DREQ
pin low level is sampled on the rising
edge of ø, 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 ø starts.
When the
DREQ
pin high level has been sampled, 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 7-31 Example of
DREQ
Pin Falling Edge 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, 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 single cycle
ends, acceptance resumes after the end of the single cycle,
DREQ
pin low level sampling is performed again, and this
operation is repeated until the transfer ends.
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