UM10503
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
993 of 1269
NXP Semiconductors
UM10503
Chapter 38: LPC43xx UART1
38.6.9 UART1 Line Status Register
The LSR is a read-only register that provides status information on the UART1 TX and RX
blocks.
4
LMS
Loopback Mode Select.
The modem loopback mode provides a mechanism to perform diagnostic loopback
testing. Serial data from the transmitter is connected internally to serial input of the
receiver. Input pin, RXD1, has no effect on loopback and output pin, TXD1 is held in
marking state. The 4 modem inputs (CTS, DSR, RI and DCD) are disconnected
externally. Externally, the modem outputs (RTS, DTR) are set inactive. Internally, the 4
modem outputs are connected to the 4 modem inputs. As a result of these
connections, the upper 4 bits of the MSR will be driven by the lower 4 bits of the MCR
rather than the 4 modem inputs in normal mode. This permits modem status interrupts
to be generated in loopback mode by writing the lower 4 bits of MCR.
0
0
Disable modem loopback mode.
1
Enable modem loopback mode.
5
-
Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
0
6
RTSEN
RTS enable.
0
0
Disable auto-rts flow control.
1
Enable auto-rts flow control.
7
CTSEN
CTS enable.
0
0
Disable auto-cts flow control.
1
Enable auto-cts flow control.
31:8
-
Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
NA
Table 858: UART1 Modem Control Register (MCR - address 0x4008 2010) bit description
Bit
Symbol
Value Description
Reset
value
Table 859: UART1 Line Status Register (LSR - address 0x4008 2014) bit description
Bit
Symbol
Value Description
Reset
value
0
RDR
Receiver Data Ready.
LSR[0] is set when the RBR holds an unread character and is cleared when the
UART1 RBR FIFO is empty.
0
0
The UART1 receiver FIFO is empty.
1
The UART1 receiver FIFO is not empty.
1
OE
Overrun Error.
The overrun error condition is set as soon as it occurs. An LSR read clears
LSR[1]. LSR[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
0
Overrun error status is inactive.
1
Overrun error status is active.