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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
279 of 808
NXP Semiconductors
UM10360
Chapter 14: LPC17xx UART0/2/3
Table 258: UARTn Line Status Register (U0LSR - address 0x4000 C014,
U2LSR - 0x4009 8014, U3LSR - 0x4009 C014, Read Only) bit description
Bit Symbol
Value Description
Reset
Value
0
Receiver
Data Ready
(RDR)
UnLSR0 is set when the UnRBR holds an unread character
and is cleared when the UARTn RBR FIFO is empty.
0
0
UnRBR is empty.
1
UnRBR contains valid data.
1
Overrun Error
(OE)
The overrun error condition is set as soon as it occurs. An
UnLSR read clears UnLSR1. UnLSR1 is set when UARTn
RSR has a new character assembled and the UARTn RBR
FIFO is full. In this case, the UARTn RBR FIFO will not be
overwritten and the character in the UARTn RSR will be lost.
0
0
Overrun error status is inactive.
1
Overrun error status is active.
2
Parity Error
(PE)
When the parity bit of a received character is in the wrong
state, a parity error occurs. An UnLSR read clears UnLSR[2].
Time of parity error detection is dependent on UnFCR[0].
Note:
A parity error is associated with the character at the top
of the UARTn RBR FIFO.
0
0
Parity error status is inactive.
1
Parity error status is active.
3
Framing Error
(FE)
When the stop bit of a received character is a logic 0, a
framing error occurs. An UnLSR read clears UnLSR[3]. The
time of the framing error detection is dependent on UnFCR0.
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 UARTn RBR FIFO.
0
0
Framing error status is inactive.
1
Framing error status is active.
4
Break
Interrupt
(BI)
When RXDn 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 RXDn goes to marking state (all
ones). An UnLSR read clears this status bit. The time of break
detection is dependent on UnFCR[0].
Note:
The break interrupt is associated with the character at
the top of the UARTn RBR FIFO.
0
0
Break interrupt status is inactive.
1
Break interrupt status is active.
5
Transmitter
Holding
Register
Empty
(THRE))
THRE is set immediately upon detection of an empty UARTn
THR and is cleared on a UnTHR write.
1
0
UnTHR contains valid data.
1
UnTHR is empty.