UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
975 of 1269
NXP Semiconductors
UM10503
Chapter 37: LPC43xx USART0_2_3
37.7.3.1 Example 1: USART_PCLK = 14.7456 MHz, BR = 9600
According to the provided algorithm DL
est
= PCLK/(16 x BR) = 14.7456 MHz / (16 x 9600)
= 96. Since this DL
est
is an integer number, DIVADDVAL = 0, MULVAL = 1, DLM = 0, and
DLL = 96.
37.7.3.2 Example 2: USART_PCLK = 12 MHz, BR = 115200
According to the provided algorithm DL
est
= PCLK/(16 x BR) = 12 MHz / (16 x 115200) =
6.51. This DL
est
is not an integer number and the next step is to estimate the FR
parameter. Using an initial estimate of FR
est
= 1.5 a new DL
est
= 4 is calculated and FR
est
is recalculated as FR
est
= 1.628. Since FRest = 1.628 is within the specified range of 1.1
and 1.9, DIVADDVAL and MULVAL values can be obtained from the attached look-up
table.
The closest value for FRest = 1.628 in the look-up
is FR = 1.625. It is
equivalent to DIVADDVAL = 5 and MULVAL = 8.
Based on these findings, the suggested USART setup would be: DLM = 0, DLL = 4,
DIVADDVAL = 5, and MULVAL = 8. According to
, the USART’s baud rate is
115384. This rate has a relative error of 0.16% from the originally specified 115200.
37.7.4 RS-485/EIA-485 modes of operation
The RS-485/EIA-485 feature allows the USART to be configured as an addressable slave.
The addressable slave is one of multiple slaves controlled by a single master.
Table 845. Fractional Divider setting look-up table
FR
DivAddVal/
MulVal
FR
DivAddVal/
MulVal
FR
DivAddVal/
MulVal
FR
DivAddVal/
MulVal
1.000
0/1
1.250
1/4
1.500
1/2
1.750
3/4
1.067
1/15
1.267
4/15
1.533
8/15
1.769
10/13
1.071
1/14
1.273
3/11
1.538
7/13
1.778
7/9
1.077
1/13
1.286
2/7
1.545
6/11
1.786
11/14
1.083
1/12
1.300
3/10
1.556
5/9
1.800
4/5
1.091
1/11
1.308
4/13
1.571
4/7
1.818
9/11
1.100
1/10
1.333
1/3
1.583
7/12
1.833
5/6
1.111
1/9
1.357
5/14
1.600
3/5
1.846
11/13
1.125
1/8
1.364
4/11
1.615
8/13
1.857
6/7
1.133
2/15
1.375
3/8
1.625
5/8
1.867
13/15
1.143
1/7
1.385
5/13
1.636
7/11
1.875
7/8
1.154
2/13
1.400
2/5
1.643
9/14
1.889
8/9
1.167
1/6
1.417
5/12
1.667
2/3
1.900
9/10
1.182
2/11
1.429
3/7
1.692
9/13
1.909
10/11
1.200
1/5
1.444
4/9
1.700
7/10
1.917
11/12
1.214
3/14
1.455
5/11
1.714
5/7
1.923
12/13
1.222
2/9
1.462
6/13
1.727
8/11
1.929
13/14
1.231
3/13
1.467
7/15
1.733
11/15
1.933
14/15