UM11029
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User manual
Rev. 1.0 — 16 June 2017
302 of 515
NXP Semiconductors
UM11029
Chapter 17: LPC84x USART0/1/2/3/4
17.6.11 USART Oversample selection register
The OSR register allows selection of oversampling in asynchronous modes. The
oversample value is the number of BRG clocks used to receive one data bit. The default is
industry standard 16x oversampling.
Changing the oversampling can sometimes allow better matching of baud rates in cases
where the peripheral clock rate is not a multiple of 16 times the expected maximum baud
rate. For all modes where the OSR setting is used, the UART receiver takes three
consecutive samples of input data in the approximate middle of the bit time. Smaller
values of OSR can make the sampling position within a data bit less accurate and may
potentially cause more noise errors or incorrect data.
17.6.12 USART Address register
The ADDR register holds the address for hardware address matching in address detect
mode with automatic address matching enabled.
17.7 Functional description
17.7.1 Clocking and baud rates
In order to use the USART, clocking details must be defined such as setting up the BRG,
and typically also setting up the FRG. See
Table 333. USART Oversample selection register (OSR, address 0x4006 4028 (USART0),
0x4006 4028 (USART1), 0x4006 8028 (USART2), 0x4007 0028 (USART3), 0x4007
4028 (USART4)) bit description
Bit
Symbol
Description
Reset
value
3:0
OSRVAL Oversample Selection Value.
0 to 3 = not supported
0x4 = 5 peripheral clocks are used to transmit and receive each data bit.
0x5 = 6 peripheral clocks are used to transmit and receive each data bit.
...
0xF= 16 peripheral clocks are used to transmit and receive each data
bit.
0xF
31:4 -
Reserved, the value read from a reserved bit is not defined.
NA
Table 334. USART Address register (ADDR, address 0x4006 402C (USART0), 0x4006 802C
(USART1), 0x4006 C02C (USART2), 0x4007 002C (USART3), 0x4007 402C
(USART4)) bit description
Bit
Symbol
Description
Reset
value
7:0
ADDRESS 8-bit address used with automatic address matching. Used when
address detection is enabled (ADDRDET in CTL = 1) and automatic
address matching is enabled (AUTOADDR in CFG = 1).
0
31:8
-
Reserved, the value read from a reserved bit is not defined.
NA