UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
951 of 1269
NXP Semiconductors
UM10503
Chapter 37: LPC43xx USART0_2_3
37.5 Pin description
37.6 Register description
The USART contains registers organized as shown in
. The Divisor Latch
Access Bit (DLAB) is contained in LCR[7] and enables access to the Divisor Latches.
Reset value reflects the data stored in used bits only. It does not include the content of
reserved bits.
Table 820. USART0/2/3 pin description
Pin function
Direction
Description
USART0
U0_RXD
I
Serial Input.
Serial receive data.
U0_TXD
O
Serial Output.
Serial transmit data.
U0_DIR
I/O
RS-485/EIA-485 output enable/direction control.
U0_UCLK
I/O
Serial clock input/output for USART0 in synchronous mode.
USART2
U2_RXD
I
Serial Input.
Serial receive data.
U2_TXD
O
Serial Output.
Serial transmit data.
U2_DIR
I/O
RS-485/EIA-485 output enable/direction control.
U2_UCLK
I/O
Serial clock input/output for USART2 in synchronous mode.
USART3
U3_RXD
I
Serial Input.
Serial receive data.
U3_TXD
O
Serial Output.
Serial transmit data.
U3_DIR
I/O
RS-485/EIA-485 output enable/direction control.
U3_UCLK
I/O
Serial clock input/output for USART3 in synchronous mode.
U3_BAUD
O
USART3 baud output.
U3_BAUD is an active LOW signal of the single clock cycle and
is generated at each rising edge of a 16x clock signal for the
transmitter section of the UART. The clock rate is established by
the USART3 clock frequency divided by the fractional divider and
the divisor specified in the baud generator divisor latches.
U3_BAUD can be used as an input to an external IrDA module.
Table 821. Register overview: USART0/2/3 (base address: 0x4008 1000, 0x400C 1000, 0x400C 2000)
Name
Access Address
offset
Description
Reset
value
Reference
RBR
RO
0x000
Receiver Buffer Register. Contains the next received
character to be read (DLAB = 0).
NA
THR
WO
0x000
Transmit Holding Register. The next character to be
transmitted is written here (DLAB = 0).
NA
DLL
R/W
0x000
Divisor Latch LSB. Least significant byte of the baud rate
divisor value. The full divisor is used to generate a baud rate
from the fractional rate divider (DLAB = 1).
0x01
DLM
R/W
0x004
Divisor Latch MSB. Most significant byte of the baud rate
divisor value. The full divisor is used to generate a baud rate
from the fractional rate divider (DLAB = 1).
0x00