UM10429
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© NXP B.V. 2010. All rights reserved.
User manual
Rev. 1 — 20 October 2010
88 of 258
NXP Semiconductors
UM10429
Chapter 10: LPC1102 Universal Asynchronous Transmitter (UART)
While the receiver is enabled (RS485CTRL bit 1 = ‘0’), all bytes received will be accepted
and stored in the RXFIFO until an address byte which does not match the
RS485ADRMATCH value is received. When this occurs, the receiver will be automatically
disabled in hardware (RS485CTRL bit 1 will be set), The received non-matching address
character will not be stored in the RXFIFO.
10.6 Architecture
The architecture of the UART is shown below in the block diagram.
The APB interface provides a communications link between the CPU or host and the
UART.
The UART receiver block, U0RX, monitors the serial input line, RXD, for valid input. The
UART RX Shift Register (U0RSR) accepts valid characters via RXD. After a valid
character is assembled in the U0RSR, it is passed to the UART RX Buffer Register FIFO
to await access by the CPU or host via the generic host interface.
The UART transmitter block, U0TX, accepts data written by the CPU or host and buffers
the data in the UART TX Holding Register FIFO (U0THR). The UART TX Shift Register
(U0TSR) reads the data stored in the U0THR and assembles the data to transmit via the
serial output pin, TXD1.
The UART Baud Rate Generator block, U0BRG, generates the timing enables used by the
UART TX block. The U0BRG clock input source is UART_PCLK. The main clock is
divided down per the divisor specified in the U0DLL and U0DLM registers. This divided
down clock is a 16x oversample clock, NBAUDOUT.
The interrupt interface contains registers U0IER and U0IIR. The interrupt interface
receives several one clock wide enables from the U0TX and U0RX blocks.
Status information from the U0TX and U0RX is stored in the U0LSR. Control information
for the U0TX and U0RX is stored in the U0LCR.
