The DMA controller is configured with user software. The setup and operation of the DMA is discussed in the following sections.
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 11-2.
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 DMASRCINCR and DMADSTINCR control bits. The DMASRCINCR bits select if the source address is incremented, decremented, or unchanged after each transfer. The DMADSTINCR 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.
DMA Transfer Modes
The DMA controller has six transfer modes selected by the DMADT bits as listed in Table 11-1. Each channel is individually configurable for its transfer mode. For example, channel 0 may be configured in single transfer mode, while channel 1 is configured for burst- block transfer mode, and channel 2 operates in repeated block mode. The transfer mode is configured independently from the addressing mode. Any addressing mode can be used with any transfer mode.
Two types of data can be transferred selectable by the DMAxCTL DSTBYTE and SRCBYTE fields. The source and/or destination location can be either byte or word data. It is also possible to transfer byte to byte, word to word, or any combination.
