Nxp semiconductors – NXP Semiconductors LPC24XX UM10237 User Manual

Page 464

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UM10237_4

User manual

Rev. 04 — 26 August 2009

464 of 792

NXP Semiconductors

UM10237

Chapter 17: LPC24XX UART1

4.17.1.1

Example 1: PCLK = 14.7456 MHz, BR = 9600

According to the 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.

4.17.1.2

Example 2: PCLK = 12 MHz, BR = 115200

According to the 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

Table 17–413

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.

4.18 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. Fractional Divider setting look-up table

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

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