Philips LPC2129 - Table 93: UART1 Interrupt Handling

UART1 157 May 03, 2004
Philips Semiconductors Preliminary User Manual
LPC2119/2129/2194/2292/2294ARM-based Microcontroller
The UART1 THRE interrupt (U1IIR3:1=001) is a third level interrupt and is activated when the UART1 THR FIFO is empty
provided certain initialization conditions have been met. These initialization conditions are intended to give the UART1 THR FIFO
a chance to fill up with data to eliminate many THRE interrupts from occurring at system start-up. The initialization conditions
implement a one character delay minus the stop bit whenever THRE=1 and there have not been at least two characters in the
U1THR at one time since the last THRE=1 event. This delay is provided to give the CPU time to write data to U1THR without a
THRE interrupt to decode and service. A THRE interrupt is set immediately if the UART1 THR FIFO has held two or more
characters at one time and currently, the U1THR is empty. The THRE interrupt is reset when a U1THR write occurs or a read of
the U1IIR occurs and the THRE is the highest interrupt (U1IIR3:1=001).
The modem interrupt (U1IIR3:1=000) is the lowest priority interrupt and is activated whenever there is any state change on
modem inputs pins, DCD, DSR or CTS. In addition, a low to high transition on modem input RI will generate a modem interrupt.
The source of the modem interrupt can be determined by examining U1MSR3:0. A U1MSR read will clear the modem interrupt.
Table 94: UART1 Interrupt Handling
U1IIR[3:0] Priority
Interrupt
Type
Interrupt
Source
Interrupt
Reset
0001 - none none -
0110 Highest
Rx Line Status /
Error
OE or PE or FE or BI U1LSR Read
0100 Second
Rx Data
Available
Rx data available or trigger level reached in FIFO mode
(FCR0=1)
U1RBR Read or
UART1 FIFO
drops below
trigger level
1100 Second
Character Time-
out Indication
Minimum of one character in the Rx FIFO and no character
input or removed during a time period depending on how many
characters are in FIFO and what the trigger level is set at (3.5
to 4.5 character times).
The exact time will be:
[(word length) X 7 - 2] X 8 + {(trigger level - number of
characters) X 8 + 1] RCLKs
U1RBR Read
0010 Third THRE THRE
U1IIR Read (if
source of
interrupt) or
THR write
0000 Fourth Modem Status CTS or DSR or RI or DCD MSR Read
note: values “0011”. “0101”, “0111”, “1000”, “1001”, “1010”, “1011”,”1101”,”1110”,”1111” are reserved.