DR
AFT
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AFT
DRAFT
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D
RAFT
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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
287 of 571
NXP Semiconductors
UM10316
Chapter 19: LPC29xx Universal Asynchronous Receiver/Transmitter
4.13 UARTn Fractional Divider Register
The UART Fractional Divider Register (U0/1FDR) controls the clock pre-scaler for the
baud rate generation and can be read and written at the user’s discretion. This pre-scaler
takes the APB clock and generates an output clock according to the specified fractional
requirements.
Important:
If the fractional divider is active (DIVADDVAL > 0) and DLM = 0, the value of
the DLL register must be 3 or greater.
a. Mode 0 (start bit and LSB are used for auto-baud)
b. Mode 1 (only start bit is used for auto-baud)
Fig 67. Autobaud 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