UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
973 of 1269
NXP Semiconductors
UM10503
Chapter 37: LPC43xx USART0_2_3
37.7.3 Baud rate calculation
USART can operate with or without using the Fractional Divider. In real-life applications it
is likely that the desired baud rate can be achieved using several different Fractional
Divider settings. The following algorithm illustrates one way of finding a set of DLM, DLL,
MULVAL, and DIVADDVAL values. Such set of parameters yields a baud rate with a
relative error of less than 1.1% from the desired one.
a. Mode 0 (start bit and LSB are used for auto-baud)
b. Mode 1 (only start bit is used for auto-baud)
Fig 115. Auto-baud a) mode 0 and b) mode 1 waveform
UARTn RX
start bit
LSB of 'A' or 'a'
U0ACR start
rate counter
start
bit0
bit1
bit2
bit3
bit4
bit5
bit6
bit7
parity stop
'A' (0x41) or 'a' (0x61)
16 cycles
16 cycles
16xbaud_rate
UARTn RX
start bit
LSB of 'A' or 'a'
rate counter
'A' (0x41) or 'a' (0x61)
start
bit0
bit1
bit2
bit3
bit4
bit5
bit6
bit7
parity stop
U1ACR start
16 cycles
16xbaud_rate