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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
202 of 368
NXP Semiconductors
UM10375
Chapter 12: LPC13xx UART
describes how to use TxEn bit in order to achieve hardware flow
control, it is strongly suggested to let UART hardware implemented auto flow control
features take care of this, and limit the scope of TxEn to software flow control.
describes how to use TXEn bit in order to achieve software flow control.
12.6.17 UART RS485 Control register (U0RS485CTRL - 0x4000 804C)
The U0RS485CTRL register controls the configuration of the UART in RS-485/EIA-485
mode.
Table 211. UART Transmit Enable Register (U0TER - address 0x4000 8030) bit description
Bit
Symbol
Description
Reset Value
6:0
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
NA
7
TXEN
When this bit is 1, as it is after a Reset, data written to the THR
is output on the TXD pin as soon as any preceding data has
been sent. If this bit cleared to 0 while a character is being sent,
the transmission of that character is completed, but no further
characters are sent until this bit is set again. In other words, a 0
in this bit blocks the transfer of characters from the THR or TX
FIFO into the transmit shift register. Software can clear this bit
when it detects that the a hardware-handshaking TX-permit
signal (CTS) has gone false, or with software handshaking,
when it receives an XOFF character (DC3). Software can set
this bit again when it detects that the TX-permit signal has gone
true, or when it receives an XON (DC1) character.
1
31:8 -
Reserved
-
Table 212. UART RS485 Control register (U0RS485CTRL - address 0x4000 804C) bit
description
Bit
Symbol
Value
Description
Reset
value
0
NMMEN
NMM enable
0
0
RS-485/EIA-485 Normal Multidrop Mode (NMM)
is disabled.
1
RS-485/EIA-485 Normal Multidrop Mode (NMM)
is enabled. In this mode, an address is detected
when a received byte causes the UART to set the
parity error and generate an interrupt.
1
RXDIS
Receiver enable
0
0
The receiver is enabled.
1
The receiver is disabled.
2
AADEN
AAD enable
0
0
Auto Address Detect (AAD) is disabled.
1
Auto Address Detect (AAD) is enabled.
3
SEL
Direction control pins select
0
0
If direction control is enabled (bit DCTRL = 1), pin
RTS is used for direction control.
1
If direction control is enabled (bit DCTRL = 1), pin
DTR is used for direction control.