TX buffer maximum
Zero byte
Programmable
threshold
Characters transmitted from
the UART
1 space
Time
DMA active periods; this
does not represent the
DMA signaling.
uart-029
Example: DMA is disabled to show the
end of the transfer and the TX buffer emptying.
TX buffer maximum
Zero byte
Programmable
threshold
8 spaces
Example: DMA is disabled to
show the end of the transfer.
Time
DMA active periods;
this does not represent
the DMA signaling.
1 character transmitted
uart-028
Functional Description
Figure 19-9. Transmit FIFO DMA Request Generation (8 Spaces)
The next example shows the setting of one space that uses the DMA for each transfer of one character to
the transmit buffer (see
). The buffer is filled faster than the baud rate at which data is
transmitted to the TX pin. Eventually, the buffer is completely full and the DMA operations stop transferring
data to the transmit buffer.
On two occasions, the buffer holds the maximum amount of data words; shortly after this, the DMA is
disabled to show the slower transmission of the data words to the TX pin. Eventually, the buffer is emptied
at the rate specified by the baud rate settings of the UARTi.UART_DLL and UARTi.UART_DLH registers.
The DMA settings must correspond to the system LH DMA controller settings to ensure correct operation
of this logic.
Figure 19-10. Transmit FIFO DMA Request Generation (1 Space)
3465
SPRUH73H – October 2011 – Revised April 2013
Universal Asynchronous Receiver/Transmitter (UART)
Copyright © 2011–2013, Texas Instruments Incorporated