Nxp Semiconductors UM10237 ユーザーズマニュアル
UM10237_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 19 December 2008
456 of 792
NXP Semiconductors
UM10237
Chapter 17: LPC24XX Universal Asynchronous Receiver/Transmitter
4.10 UART1 Line Status Register (U1LSR - 0xE001 0014, Read Only)
The U1LSR is a read-only register that provides status information on the UART1 TX and
RX blocks.
RX blocks.
Table 408: UART1 Line Status Register (U1LSR - address 0xE001 0014, Read Only) bit
description
Bit Symbol
Value Description
Reset
Value
Value
0
Receiver
Data
Ready
(RDR)
Data
Ready
(RDR)
0
U1LSR[0] is set when the U1RBR holds an unread character and
is cleared when the UART1 RBR FIFO is empty.
is cleared when the UART1 RBR FIFO is empty.
0
U1RBR is empty.
1
U1RBR contains valid data.
1
Overrun
Error
(OE)
Error
(OE)
0
The overrun error condition is set as soon as it occurs. An U1LSR
read clears U1LSR[1]. U1LSR[1] is set when UART1 RSR has a
new character assembled and the UART1 RBR FIFO is full. In
this case, the UART1 RBR FIFO will not be overwritten and the
character in the UART1 RSR will be lost.
read clears U1LSR[1]. U1LSR[1] is set when UART1 RSR has a
new character assembled and the UART1 RBR FIFO is full. In
this case, the UART1 RBR FIFO will not be overwritten and the
character in the UART1 RSR will be lost.
0
Overrun error status is inactive.
1
Overrun error status is active.
2
Parity
Error
(PE)
Error
(PE)
0
When the parity bit of a received character is in the wrong state, a
parity error occurs. An U1LSR read clears U1LSR[2]. Time of
parity error detection is dependent on U1FCR[0].
parity error occurs. An U1LSR read clears U1LSR[2]. Time of
parity error detection is dependent on U1FCR[0].
Note:
A parity error is associated with the character at the top of
the UART1 RBR FIFO.
0
Parity error status is inactive.
1
Parity error status is active.
3
Framing
Error
(FE)
Error
(FE)
0
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.
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
Framing error status is inactive.
1
Framing error status is active.
4
Break
Interrupt
(BI)
Interrupt
(BI)
0
When RXD1 is held in the spacing state (all 0’s) 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 1’s). An U1LSR
read clears this status bit. The time of break detection is
dependent on U1FCR[0].
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 1’s). 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
Break interrupt status is inactive.
1
Break interrupt status is active.