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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
304 of 808
NXP Semiconductors
UM10360
Chapter 15: LPC17xx UART1
4.11 UART1 Modem Status Register (U1MSR - 0x4001 0018, Read Only)
The U1MSR is a Read Only register that provides status information on the modem input
signals. U1MSR[3:0] is cleared on U1MSR read. Note that modem signals have no direct
effect on UART1 operation, they facilitate software implementation of modem signal
operations.
3
Framing
Error
(FE)
When the stop bit of a received character is a logic 0, a framing
error occurs. An U1LSR read clears U1LSR[3]. The time of the
framing error detection is dependent on U1FCR0. Upon detection
of a framing error, the RX will attempt to resynchronize to the data
and assume that the bad stop bit is actually an early start bit.
However, it cannot be assumed that the next received byte will be
correct even if there is no Framing Error.
Note:
A framing error is associated with the character at the top
of the UART1 RBR FIFO.
0
0
Framing error status is inactive.
1
Framing error status is active.
4
Break
Interrupt
(BI)
When RXD1 is held in the spacing state (all zeroes) for one full
character transmission (start, data, parity, stop), a break interrupt
occurs. Once the break condition has been detected, the receiver
goes idle until RXD1 goes to marking state (all ones). An U1LSR
read clears this status bit. The time of break detection is
dependent on U1FCR[0].
Note:
The break interrupt is associated with the character at the
top of the UART1 RBR FIFO.
0
0
Break interrupt status is inactive.
1
Break interrupt status is active.
5
Transmitte
r Holding
Register
Empty
(THRE)
THRE is set immediately upon detection of an empty UART1
THR and is cleared on a U1THR write.
1
0
U1THR contains valid data.
1
U1THR is empty.
6
Transmitte
r Empty
(TEMT)
TEMT is set when both U1THR and U1TSR are empty; TEMT is
cleared when either the U1TSR or the U1THR contain valid data.
1
0
U1THR and/or the U1TSR contains valid data.
1
U1THR and the U1TSR are empty.
7
Error in RX
FIFO
(RXFE)
U1LSR[7] is set when a character with a RX error such as framing
error, parity error or break interrupt, is loaded into the U1RBR.
This bit is cleared when the U1LSR register is read and there are
no subsequent errors in the UART1 FIFO.
0
0
U1RBR contains no UART1 RX errors or U1FCR[0]=0.
1
UART1 RBR contains at least one UART1 RX error.
Table 280: UART1 Line Status Register (U1LSR - address 0x4001 0014, Read Only) bit
description
Bit Symbol
Value Description
Reset
Value