UM10462
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User manual
Rev. 5.5 — 21 December 2016
265 of 523
NXP Semiconductors
UM10462
Chapter 12: LPC11U3x/2x/1x USART
12.5.17 UART Half-duplex enable register
Remark:
The HDEN register should be disabled when in smart card mode or IrDA mode
(smart card and IrDA by default run in half-duplex mode).
After reset the USART will be in full-duplex mode, meaning that both TX and RX work
independently. After setting the HDEN bit, the USART will be in half-duplex mode. In this
mode, the USART ensures that the receiver is locked when idle, or will enter a locked
state after having received a complete ongoing character reception. Line conflicts must be
handled in software. The behavior of the USART is unpredictable when data is presented
for reception while data is being transmitted.
For this reason, the value of the HDEN register should not be modified while sending or
receiving data, or data may be lost or corrupted.
12.5.18 Smart Card Interface Control register
This register allows the USART to be used in asynchronous smart card applications.
Table 250. USART Transmit Enable Register (TER - 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 251. USART Half duplex enable register (HDEN - addresses 0x4000 8040) bit
description
Bit
Symbol
Value
Description
Reset
value
0
HDEN
Half-duplex mode enable
0
0
Disable half-duplex mode.
1
Enable half-duplex mode.
31:1
-
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is not
defined.
-