AMD Am186 CC User Manual page 149

The DMA synchronization for the channel ("Setting Synchronization" on page 8-17)
Whether DMA transfers use buffer queues or circular buffers (see "Using Buffer Queues
or Circular Buffers" on page 8-20)
8.5.6.6.1 Generating Interrupts
The general-purpose DMA channels can generate an interrupt request when the terminal
count value in the GDxTC register reaches 0. To program this feature, set the INT bit in the
GDxCON0 register to 1.
8.5.6.6.2 Transferring Bytes or Words
The TS bit in the GDxCON0 register can enable either byte or word transfers.
8.5.6.6.3 Incrementing or Decrementing Addresses
The source and destination addresses can increment or decrement after each transfer, or
remain constant. Specify the action with the SINC and DINC bits in the GD x CON1 register.
The increment or decrement factor of the source and destination addresses are
programmed independently; however, both the source and destination have to be the same
size. Word transfers are only supported when the address is incremented or decremented
by 2 (an increment by one causes unpredictable results). Byte transfers can be incremented
or decremented by 1 or 2. When a byte transfer is incremented or decremented by 2, the
high byte is ignored.
Because the DMA controller stores addresses as 20-bit linear values, there are no segment
restrictions on the address increment and decrement. However, when using the circular
buffer feature, the address boundary is limited to the size of the buffer. For example, when
using a 1-Kbyte circular buffer, the address has to start at a 1-Kbyte boundary. For more
information, see "Using Buffer Queues or Circular Buffers" on page 8-20.
8.5.6.6.4 Selecting DMA Request Sources
The DSEL bit field in the GDxCON0 register sets the DMA request source for that channel.
As shown in Figure 8-3, the DMA request source can be an external DRQ signal, Timer 2,
UART receiver, UART transmitter, High-Speed UART receiver, or High-Speed UART
transmitter.
The Am186CC and Am186CU microcontrollers also support USB endpoints A, B, C, or D
CC CU
as request sources. Each USB endpoint can be configured either for receive or transmit.
In addition to setting the DMA request source, the DSEL bit field also selects the
synchronization type (see "Setting Synchronization" on page 8-17).
DMA Controller
Am186™CC/CH/CU Microcontrollers User's Manual 8-15