
UM10800
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© NXP Semiconductors N.V. 2016. All rights reserved.
User manual
Rev. 1.2 — 5 October 2016
188 of 487
NXP Semiconductors
UM10800
Chapter 13: LPC82x USART0/1/2
13.5 General description
The USART receiver block monitors the serial input line, Un_RXD, for valid input. The
receiver shift register assembles characters as they are received, after which they are
passed to the receiver buffer register to await access by the CPU or the DMA controller.
When RTS signal is configured as an RS-485 output enable, it is asserted at the
beginning of an transmitted character, and de-asserted either at the end of the character,
or after a one character delay (selected by software).
The USART transmitter block accepts data written by the CPU or DMA controllers and
buffers the data in the transmit holding register. When the transmitter is available, the
transmit shift register takes that data, formats it, and serializes it to the serial output,
Un_TXD.
U0_CTS
I
external
to pin
any pin
PINASSIGN0
Clear To Send input for USART0. Active low signal
indicates that the external device that is in
communication with the USART is ready to accept
data. This feature is active when enabled by the
CTSEn bit in CFG register and when configured to
appear on a device pin. When de-asserted (high) by
the external device, the USART will complete
transmitting any character already in progress, then
stop until CTS is again asserted (low).
U0_SCLK
I/O
external
to pin
any pin
PINASSIGN1
Serial clock input/output for USART0 n synchronous
mode.
U1_TXD
O
external
to pin
any pin
PINASSIGN1
Transmitter output for USART1. Serial transmit data.
U1_RXD
I
external
to pin
any pin
PINASSIGN1
Receiver input for USART1.
U1_RTS
O
external
to pin
any pin
PINASSIGN1
Request To Send output for USART1.
U1_CTS
I
external
to pin
any pin
PINASSIGN2
Clear To Send input for USART1.
U1_SCLK
I/O
external
to pin
any pin
PINASSIGN2
Serial clock input/output for USART1 in synchronous
mode.
U2_TXD
O
external
to pin
any pin
PINASSIGN2
Transmitter output for USART2. Serial transmit data.
U2_RXD
I
external
to pin
any pin
PINASSIGN2
Receiver input for USART2.
U2_RTS
O
external
to pin
any pin
PINASSIGN3
Request To Send output for USART2.
U2_CTS
I
external
to pin
any pin
PINASSIGN3
Clear To Send input for USART2.
U2_SCLK
I/O
external
to pin
any pin
PINASSIGN3
Serial clock input/output for USART2 in synchronous
mode.
Table 174. USART pin description
Function
I/O
Type
Connect
to
Use register
Reference
Description