UM10503
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User manual
Rev. 1.3 — 6 July 2012
996 of 1269
NXP Semiconductors
UM10503
Chapter 38: LPC43xx UART1
38.6.13 UART1 Fractional Divider Register
The UART1 Fractional Divider Register (FDR) 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 greater than 2.
This register controls the clock pre-scaler for the baud rate generation. The reset value of
the register keeps the fractional capabilities of UART1 disabled making sure that UART1
is fully software and hardware compatible with UARTs not equipped with this feature.
Table 862: Autobaud Control Register (ACR - address 0x4008 2020) bit description
Bit
Symbol
Value Description
Reset value
0
START
Auto-baud start bit.
This bit is automatically cleared after auto-baud completion.
0
0
Auto-baud stop (auto-baud is not running).
1
Auto-baud start (auto-baud is running). Auto-baud run bit. This bit is
automatically cleared after auto-baud completion.
1
MODE
Auto-baud mode select bit.
0
0
Mode 0.
1
Mode 1.
2
AUTORESTART
Auto-baud restart bit.
0
0
No restart
1
Restart in case of time-out (counter restarts at next UART1 Rx falling
edge)
7:3
-
-
Reserved, user software should not write ones to reserved bits. The value
read from a reserved bit is not defined.
0
8
ABEOINTCLR
End of auto-baud interrupt clear bit (write-only).
0
0
Writing a 0 has no impact.
1
Writing a 1 will clear the corresponding interrupt in the IIR.
9
ABTOINTCLR
Auto-baud time-out interrupt clear bit (write-only).
0
0
Writing a 0 has no impact.
1
Writing a 1 will clear the corresponding interrupt in the IIR.
31:10 -
-
Reserved, user software should not write ones to reserved bits. The value
read from a reserved bit is not defined.
0
Table 863: UART1 Fractional Divider Register (FDR - address 0x4008 2028) bit description
Bit
Function
Description
Reset value
3:0
DIVADDVAL
Baud-rate generation pre-scaler divisor value. If this field is 0,
fractional baud-rate generator will not impact the UARTn
baudrate.
0
7:4
MULVAL
Baud-rate pre-scaler multiplier value. This field must be
greater or equal 1 for UARTn to operate properly, regardless
of whether the fractional baud-rate generator is used or not.
1
31:8
-
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
0