Section 7 DMA Controller (DMAC)
Rev. 3.00 Mar. 14, 2006 Page 203 of 804
REJ09B0104-0300
7.8
Notes on Usage
1. DMAC Register Access During Operation
Except for clearing the DTE bit in DMDR, the settings for channels being transferred
(including waiting state) must not be changed. The register settings must be changed during
the transfer prohibited state.
2. Settings of Module Stop Function
The DMAC operation can be enabled or disabled by the module stop control register. The
DMAC is enabled by the initial value.
Setting bit MSTPA13 in MSTPCRA stops the clock supplied to the DMAC and the DMAC
enters the module stop state. However, when a transfer for a channel is enabled or when an
interrupt is being requested, bit MSTPA13 cannot be set to 1. Clear the DTE bit to 0, clear the
DTIF or DTIE bit in DMDR to 0, and then set bit MSTPA13.
When the clock is stopped, the DMAC registers cannot be accessed. However, the following
register settings are valid in the module stop state. Disable them before entering the module
stop state, if necessary.
TENDE bit in DMDR is 1 (the TEND signal output enabled)
DACKE bit in DMDR is 1 (the DACK signal output enabled)
3. Activation by
DREQ
Falling Edge
The
DREQ
falling edge detection is synchronized with the DMAC internal operation.
A. Activation request waiting state: Waiting for detecting the
DREQ
low level. A transition to
2. is made.
B. Transfer waiting state: Waiting for a DMAC transfer. A transition to 3. is made.
C. Transfer prohibited state: Waiting for detecting the
DREQ
high level. A transition to 1. is
made.
After a DMAC transfer enabled, a transition to 1. is made. Therefore, the
DREQ
signal is
sampled by low level detection at the first activation after a DMAC transfer enabled.
4. Acceptation of Activation Source
At the beginning of an activation source reception, a low level is detected regardless of the
setting of
DREQ
falling edge or low level detection. Therefore, if the
DREQ
signal is driven
low before setting DMDR, the low level is received as a transfer request.
When the DMAC is activated, clear the
DREQ
signal of the previous transfer.
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