UART/IrDA Functional Description
12-94
In receive mode, a DMA request is generated as soon as the receive FIFO
reaches its threshold. This request is deasserted when the number of bytes
defined by the threshold level has been read by the system DMA.
Figure 12–21. Transmit FIFO DMA Request Generation
Programmable threshold
Transmit FIFO level
Zero byte
time
DMA request
time
DMA request
Transmit FIFO level
Full level
active low
Threshold writes
from system DMA
Number
of spaces
In transmit mode, a DMA request is automatically asserted when FIFO is
empty. This request is deasserted when the number of bytes defined by the
threshold level has been written by the system DMA. The DMA request is
again asserted if the FIFO is able to receive the number of bytes defined by
the threshold.