STR720 datasheet(174/401 Pages) STMICROELECTRONICS

174 / 401 page

STR720 - UART

174/401

16.3.5

Baud rate generation

The baud rate generator provides a clock at 16 times the baud rate, called the oversampling

clock. This clock only ticks if ASCControl(Run) is set to’1’. Setting this bit to 0 will

immediately freeze the state of the ASCs transmitter and receiver. This should only be done

when the ASC is idle.

The baud rate and the required reload value for a given baud rate can be determined by the

following formulae:

Baudrate = fAPB / (16 * <ASCBaudRate>)

<ASCBaudRate> = fAPB / (16 * Baudrate)

where: <ASCBaudRate> represents the content of the ASCBaudRate register, taken as

unsigned 16-bit integer, and fAPB is the clock frequency of the APB sub-system to which

UART block is connected.

The following tables list various commonly used baud rates together with the required reload

values and the deviation errors for various different APB clock frequencies..

Table 43. Baud rates with fAPB = 16 MHz

Baud rate

Reload value

(exact)

Reload value

(integer)

Reload value

(hex)

Deviation error

625K

1.6

0002

20%

38.4K

26.042

001A

0.160%

19.2K

52.083

0034

0.160%

9600

104.167

104

0068

0.160%

4800

208.333

208

00D0

0.160%

2400

416.667

417

01A1

0.080%

1200

833.333

833

0341

0.040%

600

1666.667

1667

0683

0.020%

300

3333.333

3333

0D05

0.010%

13333.333

13333

3415

0.003%

Table 44. Baud rates with fAPB = 20 MHz

Baud rate

Reload value

(exact)

Reload value

(integer)

Reload value

(hex)

Deviation error

625K2

20002

38.4K

32.552

0021

1.358%

19.2K

65.104

0041

0.160%

9600

130.208

130

0082

0.160%

4800

260.417

260

0104

0.160%

2400

520.833

521

0209

0.032%

1200

1041.667

1042

0412

0.032%

600

2083.333

2083

0823

0.016%

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