ST20-GP1 datasheet(77/116 Pages) STMICROELECTRONICS

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ST20-GP1

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13.3.1 Baud rates

The baud rate generator provides a clock at 16 times the baud rate. The baud rate and the required

reload value for a given baud rate can be determined by the following formulas:

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

16-bit integer,

fCPU is the frequency of the CPU.

Note that altering the CPU speed selection pins will thus change the baud rate. Software can

accommodate this by reading the SysRatio register, see section 10.3, in calculating the CPU

frequency.

The table below lists various commonly used baud rates together with the required reload values

and the deviation errors for the ST20-GP1 using a CPU clock of 33.736 MHz.

Note: The deviation errors given in the table above are rounded.

13.4 Interrupt control

The ASC contains two registers that are used to control interrupts, the status register (ASCStatus)

and the interrupt enable register (ASCIntEnable). The status bits in the ASCStatus register

determine the cause of the interrupt. Interrupts will occur when a status bit is 1 (high) and the

corresponding bit in the ASCIntEnable register is 1.

The error interrupt signal (ErrorInterrupt) is generated by the ASC from the OR of the parity error,

framing error, and overrun error status bits after they have been ANDed with the corresponding

enable bits in the ASCIntEnable register.

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 13.1 Baud rates

Baud rate =

16 (<ASCBaudRate>)

<ASCBaudRate> = (

16 x Baud rate

)

fCPU

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