UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 464 o f 792
NXP Semiconductors UM10237
Chapter 17: LPC24XX Universal Asynchronous Receiver/Transmitter
4.16.1.1 Example 1: PCLK = 14.7456 MHz, BR = 9600
According to the the provided algorithm DLest = PCLK/(16 x BR) = 14.7456 MHz / (16 x
9600) = 96. Since this DLest is an integer number, DIVADDVAL= 0, MULVAL = 1,
DLM = 0, and DLL = 96.
4.16.1.2 Example 2: PCLK = 12 MHz, BR = 115200
According to the the provided algorithm DLest = PCLK/(16 x BR) = 12 MHz / (16 x 115200)
= 6.51. This DLest is not an integer number and the next step is to estimate the FR
parameter. Using an initial estimate of FRest = 1.5 a new DLest = 4 is calculated and FRest
is recalculated as FRest = 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 Table17–413 is FR = 1.625. It is
equivalent to DIVADDVAL= 5 and MULVAL = 8.
Based on these findings, the suggested UART setup would be: DLM = 0, DLL = 4,
DIVADDVAL= 5, and MULVAL = 8. According to Equation 17–5 UART’s is 115384. This
rate has a relative error of 0.16% from the originally specified 115200.
4.17 UART1 Transmit Enable Register (U1TER - 0xE001 0030)
In addition to being equipped with full hardware flow control (auto-cts and auto-rts
mechanisms described above), U1TER enables implementation of software flow control,
too. When TxEn=1, UART1 transmitter will keep sending data as long as they are
available. As soon as TxEn becomes 0, UART1 transmission will stop.
Table 413. Fraction al 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