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Chapter 26 DMA Controller
3.DMA Controller (DMAC) Operation
● Transfer count register reloading
After transfer is performed the specified number of times, the initial value is set in the transfer count register again
and waiting for a start request starts.
Set this type of reloading when the entire transfer sequence is to be performed repeatedly.
If reload is not specified, the count register value remains 0 after the transfer is performed the specified number of
times and no further transfer is performed.
● Transfer source address register reloading
After transfer is performed the specified number of times, the initial value is set in the transfer source address
register again.
Set this type of reloading when transfer is to be repeated from a fixed area in the transfer source address area.
If reload is not specified, the transfer source address register value after the transfer is performed the specified
number of times becomes the next address. Use this type when the address area is not fixed.
● Transfer destination address register reloading
After transfer is performed the specified number of times, the initial value is set in the transfer destination address
register again.
Set this type of reloading when transfer is to be repeated to a fixed area in the transfer destination address area.
(The processing hereafter is the same as described in "Transfer source address register reloading" above.)
• If only reloading of the transfer source/transfer destination register is enabled, restart after transfer is
performed the specified number of times is not implemented and only the values of each address register are
set.
● Special examples of operating mode and the reload operation
• If transfer is performed in continuous transfer mode by external pin input level detection and transfer count
register reloading is used, transfer continues by reloading even though transfer ends during continuous input.
Also in this case, an end code is set.
• If it is preferable that processing stops when data transfer ends and starts after input is detected again, do not
specify reload.
• For a transfer in burst, block, or step transfer mode, transfer stops temporarily after reload when data transfer
ends. Transfer does not start until new transfer request input is detected.
3.4 Addressing Mode
Specify the transfer destination/transfer source address independently for each transfer chan-
nel.
■ Address Register Specifications
The following two methods are provided to specify an address register. The method specified depends on the
transfer sequence.
• In 2-cycle transfer mode, set the transfer source address in the transfer source address setting register
(DMADA) and the transfer destination address in the transfer destination address setting register (DMASA).
• In fly-by transfer mode, specify the memory address in the transfer destination address setting register
(DMASA). In this case, the value in the transfer source address setting register (DMADA) is ignored.