UART/Autobaud Control and Status Registers
12-33
UART Devices
The transmission control register (TCR) stores the receive FIFO threshold
levels to start/stop transmission during hardware/software flow control.
Table 12–34. Transmission Control Register (TCR)
Bit
Name
Function
R/W
Reset
Value
7–4
RX_FIFO_TRIG_START
RCV FIFO trigger level to RESTORE
transmission (0 – 60)
R/W
0000
3–0
RX_FIFO_TRIG_HALT
RCV FIFO trigger level to HALT transmission
(0 – 60)
R/W
1111
Notes:
1) Trigger levels from 0 - 60 bytes are available with a granularity of four
(Trigger level = 4 x [4-bit register value]).
2) The programmer must ensure that TCR[3:0] > TCR[7:4] whenever automatic RTS or software flow control is
enabled to avoid a faulty operation of the device.
3) In FIFO interrupt mode with flow control, programmer must also ensure that trigger level to HALT transmission is
greater or equal to receive FIFO trigger level (either TLR[7:4] or FCR[7:6]): otherwise, FIFO operation stalls. In FIFO
DMA mode with flow control, this issue does not exist because a DMA request is sent each time a byte is received.
The trigger level register (TLR) stores the programmable transmit and receive
FIFO trigger levels used for DMA and IRQ generation.
Table 12–35. Trigger Level Register (TLR)
Bit
Name
Function
R/W
Reset
Value
7–4
RX_FIFO_TRIG_DMA
Receive FIFO trigger level
R/W
0000
3–0
TX_FIFO_TRIG_DMA
Transmit FIFO trigger level
R/W
0000