UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
968 of 1269
NXP Semiconductors
UM10503
Chapter 37: LPC43xx USART0_2_3
After reset RS485 mode will be disabled. The RS485 feature allows the USART to be
configured as one of multiple addressable slave receivers controlled by a single USART.
In RS485 mode the USART differentiates between an address character and a data
character by means of a ninth bit. The parity bit is used to implement this bit, and when set
to ‘1’ indicates an address and when set to ‘0’ indicates data. RS485 mode is enabled by
setting the NMMEN bit. The USART slave receiver can be assigned a unique address
and, manually or automatically, reject or accept data based on a received address. See
section
for details.
37.6.17 USART RS485 Address Match register
The RS485ADRMATCH register contains the address match value for RS-485/EIA-485
mode.
The
ADRMATCH
bit field contains the slave address match value that is used to compare a
received address value to. During automatic address detection, this value is used to
accept or reject serial input data.
3
-
-
Reserved.
-
4
DCTRL
Direction control for DIR pin.
0
0
Disable Auto Direction Control.
1
Enable Auto Direction Control.
5
OINV
Direction control pin polarity.
This bit reverses the polarity of the direction
control signal on the DIR pin.
0
0
The direction control pin will be driven to logic ‘0’
when the transmitter has data to be sent. It will be
driven to logic ‘1’ after the last bit of data has been
transmitted.
1
The direction control pin will be driven to logic ‘1’
when the transmitter has data to be sent. It will be
driven to logic ‘0’ after the last bit of data has been
transmitted.
31:6 -
-
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit
is not defined.
NA
Table 840. USART RS485 Control register (RS485CTRL - addresses 0x4008 104C (USART0),
0x400C 104C (USART2), 0x400C 204C (USART3)) bit description
…continued
Bit
Symbol
Value
Description
Reset
value
Table 841. USART RS485 Address Match register (RS485ADRMATCH - addresses
0x4008 1050 (USART0), 0x400C 1050 (USART2), 0x400C 2050 (USART3)) bit
description
Bit
Symbol
Description
Reset value
7:0
ADRMATCH
Contains the address match value.
0x00
31:8
-
Reserved
-