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8-4
8.2 DMA Operation
The DMA controller is configured with user software. The setup and operation
of the DMA is discussed in the following sections.
8.2.1 DMA Addressing Modes
The DMA controller has four addressing modes. The addressing mode for
each DMA channel is independently configurable. For example, channel 0
may transfer between two fixed addresses, while channel 1 transfers between
two blocks of addresses. The addressing modes are shown in Figure 8−2. The
addressing modes are:
- Fixed address to fixed address
- Fixed address to block of addresses
- Block of addresses to fixed address
- Block of addresses to block of addresses
The addressing modes are configured with the DMASRCINCRx and
DMADSTINCRx control bits. The DMASRCINCRx bits select if the source
address is incremented, decremented, or unchanged after each transfer. The
DMADSTINCRx bits select if the destination address is incremented,
decremented, or unchanged after each transfer.
Transfers may be byte-to-byte, word-to-word, byte-to-word, or word-to-byte.
When transferring word-to-byte, only the lower byte of the source-word
transfers. When transferring byte-to-word, the upper byte of the
destination-word is cleared when the transfer occurs.
Figure 8−2. DMA Addressing Modes
Address SpaceAddress Space
DMA
Controller
Address Space Address Space
DMA
Controller
DMA
Controller
DMA
Controller
Fixed Address To Block Of Addresses
Fixed Address To Fixed Address
Block Of Addresses To Fixed Address
Block Of Addresses To Block Of Addresses