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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
308 of 808
NXP Semiconductors
UM10360
Chapter 15: LPC17xx UART1
5. If Mode = 0 then the rate counter will stop on next falling edge of the UART1 Rx pin. If
Mode = 1 then the rate counter will stop on the next rising edge of the UART1 Rx pin.
6. The rate counter is loaded into U1DLM/U1DLL and the baud-rate will be switched to
normal operation. After setting the U1DLM/U1DLL the end of auto-baud interrupt
U1IIR ABEOInt will be set, if enabled. The U1RSR will now continue receiving the
remaining bits of the “A/a” character.
4.16 UART1 Fractional Divider Register (U1FDR - 0x4001 0028)
The UART1 Fractional Divider Register (U1FDR) 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 2 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 48. 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