Number
of
spaces
Programmable FIFO threshold
TX FIFO level
Zero byte
Time
Interrupt request
Time
Interrupt request
active high
Full level
uart-025
Functional Description
Figure 19-6. TX FIFO Interrupt Request Generation
In transmit mode, an interrupt request is automatically asserted when the TX FIFO is empty. This request
is deasserted when the TX FIFO crosses the threshold level. The interrupt line is deasserted until a
sufficient number of elements is transmitted to go below the TX FIFO threshold.
19.3.6.3 FIFO Polled Mode Operation
In FIFO polled mode (the UARTi.UART_FCR[0] FIFO_EN bit is set to 0 and the relevant interrupts are
disabled by the UARTi.UART_IER register), the status of the receiver and transmitter can be checked by
polling the line status register (UARTi.UART_LSR).
This mode is an alternative to the FIFO interrupt mode of operation in which the status of the receiver and
transmitter is automatically determined by sending interrupts to the MPU.
19.3.6.4 FIFO DMA Mode Operation
Although DMA operation includes four modes (DMA modes 0 through 3), assume that mode 1 is used.
(Mode 2 and mode 3 are legacy modes that use only one DMA request for each module.)
In mode 2, the remaining DMA request is used for RX. In mode 3, the remaining DMA request is used for
TX.
DMA requests in mode 2 and mode 3 use the following signals:
•
S_DMA_48
•
S_DMA_50
•
S_DMA_52/D_DMA_10
•
S_DMA_54
The following signals are not used by the module in mode 2 and mode 3:
•
S_DMA_49
•
S_DMA_51
•
S_DMA_53/D_DMA_11
•
S_DMA_55
3462
Universal Asynchronous Receiver/Transmitter (UART)
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated