
DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
315 of 808
NXP Semiconductors
UM10360
Chapter 15: LPC17xx UART1
The driver delay time is the delay between the last stop bit leaving the TXFIFO and the
de-assertion of RTS (or DTR). This delay time can be programmed in the 8-bit RS485DLY
register. The delay time is in periods of the baud clock. Any delay time from 0 to 255 bit
times may be programmed.
RS485/EIA-485 output inversion
The polarity of the direction control signal on the RTS (or DTR) pins can be reversed by
programming bit 5 in the U1RS485CTRL register. When this bit is set, the direction control
pin will be driven to logic 1 when the transmitter has data waiting to be sent. The direction
control pin will be driven to logic 0 after the last bit of data has been transmitted.
4.22 UART1 FIFO Level register (U1FIFOLVL - 0x4001 0058, Read Only)
U1FIFOLVL register is a Read Only register that allows software to read the current FIFO
level status. Both the transmit and receive FIFO levels are present in this register.
5.
Architecture
The architecture of the UART1 is shown below in the block diagram.
The APB interface provides a communications link between the CPU or host and the
UART1.
The UART1 receiver block, U1RX, monitors the serial input line, RXD1, for valid input.
The UART1 RX Shift Register (U1RSR) accepts valid characters via RXD1. After a valid
character is assembled in the U1RSR, it is passed to the UART1 RX Buffer Register FIFO
to await access by the CPU or host via the generic host interface.
The UART1 transmitter block, U1TX, accepts data written by the CPU or host and buffers
the data in the UART1 TX Holding Register FIFO (U1THR). The UART1 TX Shift Register
(U1TSR) reads the data stored in the U1THR and assembles the data to transmit via the
serial output pin, TXD1.
The UART1 Baud Rate Generator block, U1BRG, generates the timing enables used by
the UART1 TX block. The U1BRG clock input source is the APB clock (PCLK). The main
clock is divided down per the divisor specified in the U1DLL and U1DLM registers. This
divided down clock is a 16x oversample clock, NBAUDOUT.
The modem interface contains registers U1MCR and U1MSR. This interface is
responsible for handshaking between a modem peripheral and the UART1.
Table 290. UART1 FIFO Level register (U1FIFOLVL - address 0x4001 00458, Read Only) bit
description
Bit
Symbol
Description
Reset
value
3:0
RXFIFILVL
Reflects the current level of the UART1 receiver FIFO.
0 = empty, 0xF = FIFO full.
0x00
7:4
-
Reserved. The value read from a reserved bit is not defined.
NA
11:8
TXFIFOLVL
Reflects the current level of the UART1 transmitter FIFO.
0 = empty, 0xF = FIFO full.
0x00
31:12
-
Reserved. The value read from a reserved bit is not defined.
NA