UART/Autobaud Functional Description
12-39
UART Devices
12.5.2 Trigger Levels
The UART provides programmable trigger levels for both receiver and trans-
mitter DMA and interrupt generation. After reset, both transmitter and receiver
FIFOs are disabled (in effect, the trigger level is the default value of one byte).
Programmable trigger level is an enhanced feature available via the trigger
level register (TLR).
12.5.3 Interrupts
The UART generates interrupts on the UART_nIRQ output pin. All interrupts
can be enabled/disabled by writing to the appropriate bit in the interrupt enable
register (IER). The interrupt status of the device can be checked at any time
by reading the interrupt identification register (IIR).
12.5.3.1 Generic Interrupts Description
There are seven possible interrupts, prioritized to six different levels.
When an interrupt is generated, the interrupt identification register (IIR) indi-
cates a pending interrupt by bringing IIR[0] to logic 0, and it specifies the type
of interrupt through IIR[5 - 1]. Table 12–42 summarizes the interrupt control
functions.
Table 12–42. Generic Interrupt Descriptions in Modem Mode
IIR[5 - 0]
Priority
Level
Interrupt
Type
Interrupt Source
Interrupt Reset Method
0 0 0 0 0 1
None
None
None
None
0 0 0 1 1 0
1
Receiver line
status
OE, FE, PE, or BI errors occur
in characters in the RX FIFO
FE, PE, BI: All erroneous
characters are read form the
RX FIFO. OE: Read LSR
0 0 1 1 0 0
2
RX time-out
Stale data in RX FIFO
Read RHR
0 0 0 1 0 0
2
RHR interrupt
DRDY (data ready)
(FIFO disable)
RX FIFO above trigger level
(FIFO enable)
Read RHR until interrupt
condition disappears.
0 0 0 0 1 0
3
THR interrupt
TFE (THR empty)
(FIFO disable)
TX FIFO below trigger level
(FIFO enable)
Write to THR until interrupt
condition disappears.
0 0 0 0 0 0
4
Modem status
MSR1:0/ = 0
Read MSR