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16.4
Setting Up Transfer Request
The following two types of transfer requests can be used to start DMA transfer. The
software request can be used at any time regardless of other request settings.
■ Internal Peripheral Request
The transfer request is generated by an interrupt from an internal peripheral circuit.
Which peripheral interrupt requests generates a transfer request can be set independently for each channel
(DMACA: IS4 to IS0 =1xxxx
Note:
As interrupt request used to generate transfer requests are also passed to the CPU as interrupt
requests, always disable these interrupts in the interrupt controller. (ICR register)
■ Software Request
Writing to the trigger bit in the register generates the transfer request. (DMACA:STRG)
This is independent of the above transfer requests and is always available.
If a software request is set at the same time as transfer is enabled, the DMA transfer request to the bus
controller is outputted immediately and transfer starts.
Note:
If a software request is issued to a channel that is also set the internal peripheral request, a factor
clear signal is sent to the peripheral when the transfer completes. As this may clear an existing
transfer request, do not use the software transfer request function in this case.
).
B
CHAPTER 16 DMAC (DMA Controller)
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