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13.4 Operations of the DMA Controller
13.4.7 DMA Transfer Start And Pause
DMA transfer start is controlled independently on each channel. However, all channels
should be enabled in the general register.
Pause DMA transfer in the following cases:
Pause setting in the control register
NMI/hold suppression level interrupt processing
s DMA Transfer Start
r Enabling all channels
Before activating each DMAC channel, enable all channels using the DMA enable bit (DMAE).
If the bit is not set, any activation setting or transfer request will be invalid.
r Activating transfer
Set the transfer enable bit in the control register of each channel to activate transfer. When a
transfer request to the activated channel is received, DMA transfer starts in the specified mode.
r Activating from pause status
If transfer is paused on each or all channels before activation, transfer activation does not clear
the pause status and no transfer request is accepted. To accept a transfer request, release the
pause status first.
s Acceptance of Transfer Request and Transfer
The set transfer requirements are sampled from each channel after activation. If a transfer
request is detected, the request is held in the DMAC until the transfer request clear conditions
are satisfied.
A transfer request is always received even when transfer processing is executed on a transfer
request from another channel.
After each unit of transfer, the next processing channel is
determined by checking the priority.
s Pause of DMA Transfer
r Pausing by writing the control register
Set each channel independently or all channels simultaneously.
If the halt bit is set, transfer on the corresponding channel is paused until the setting is cleared.
Transfer starts again when the pause status is cleared.
r NMI/hold suppression level interrupt processing
If an NMI or an interrupt request of a higher level than the hold suppression level is generated,
the DMAC pauses all the current transfer channels at a boundary between units of transfer and
releases the bus privilege to give priority to NMI/interrupt processing.
The DMAC holds a