ST20-GP6 datasheet(86/123 Pages) STMICROELECTRONICS

86 / 123 page

ST20-GP6

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

ing formulae:

where: <ASCBaudRate> represents the content of the

ASCBaudRate register, taken as unsigned

16-bit integer,

fCPU is the frequency of the CPU.

Table 15.3 lists various commonly used baud rates together with the required reload values and the

rounded deviation errors for an example baud rate with a CPU clock of 32.736 MHz.

15.4 Interrupt control

The ASC has a single interrupt coming out of it, called

ASC_interrupt. The status bits in the ASC-

Status register determine the cause of the interrupt. ASC_interrupt will go high when a status bit

is 1 (high) and the corresponding bit in the

ASCIntEnable register is 1.

Note the status register

cannot be written to directly by software. The reset mechanism for the sta-

tus register is described below.

The following diagram illustrates the situation.

Baud rate

Reload value

(exact)

Reload value

(integer)

Reload value

(hex)

Deviation error

38400

53.28125

-0.53%

28800

71.04167

-0.06%

19200

106.5625

107

0.41%

14400

142.0833

142

-0.06%

9600

213.125

213

-0.06%

4800

426.25

426

1AA

-0.06%

2400

852.5

853

355

0.06%

1200

1705

6A9

0.00%

600

3410

D52

0.00%

300

6820

1AA4

0.00%

27280

6A90

0.00%

Table 15.3 Baud rates

Baudrate =

16 (<ASCBaudRate>)

<ASCBaudRate> = (

16 x Baudrate

)

fCPU

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