DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
288 of 571
NXP Semiconductors
UM10316
Chapter 19: LPC29xx Universal Asynchronous Receiver/Transmitter
This register controls the clock pre-scaler for the baud rate generation. The reset value of
the register keeps the fractional capabilities of the UARTs disabled making sure that the
UART is fully software and hardware compatible with UARTs not equipped with this
feature.
The UART baudrate can be calculated as (n = 0/1):
(2)
Where UARTCLK is the peripheral clock (BASE_UART_CLK), U0/1DLM and U0/1DLL
are the standard UART0/1 baud rate divider registers, and DIVADDVAL and MULVAL are
UART0/1 fractional baudrate generator specific parameters.
The value of MULVAL and DIVADDVAL should comply to the following conditions:
1. 0 < MULVAL
≤
15
2. 0
≤
DIVADDVAL
<
15
3. DIVADDVAL<MULVAL
The value of the U0/1FDR should not be modified while transmitting/receiving data or data
may be lost or corrupted.
If the U0/1FDR register value does not comply to these two requests, then the fractional
divider output is undefined. If DIVADDVAL is zero then the fractional divider is disabled,
and the clock will not be divided.
4.13.1 Baudrate calculation
UART can operate with or without using the Fractional Divider. In real-life applications it is
likely that the desired baudrate 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 baudrate with a
relative error of less than 1.1% from the desired one.
Table 244. UARTn Fractional Divider Register (U0FDR - address 0xE004 5028,
U1FDR - 0xE004 6028) bit description
Bit
Function
Value Description
Reset
value
3:0
DIVADDVAL
0
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
1
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
-
NA
Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined.
0
UARTn
baudrate
UARTCLK
16
256
UnDLM
×
UnDLL
+
(
)
×
1
DivAddVal
MulVal
-----------------------------
+
⎝
⎠
⎛
⎞
×
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=