ST20-GP1 View Datasheet(PDF) - STMicroelectronics
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ST20-GP1 Datasheet PDF : 116 Pages
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ST20-GP1
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:
Baud rate =
fCPU
16 (<ASCBaudRate>)
<ASCBaudRate> = (
fCPU
)
16 x Baud rate
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.
Baud rate
Reload value
(exact)
Reload value
(integer)
Reload value
(hex)
38400
28800
19200
14400
9600
4800
2400
1200
600
300
75
53.28125
71.04167
106.5625
142.0833
213.125
426.25
852.5
1705
3410
6820
27280
53
71
107
142
213
426
853
1705
3410
6820
27280
35
47
6B
8E
D5
1AA
355
6A9
D52
1AA4
6A90
Table 13.1 Baud rates
Note: The deviation errors given in the table above are rounded.
Deviation error
-0.53%
-0.06%
0.41%
-0.06%
-0.06%
-0.06%
0.06%
0.00%
0.00%
0.00%
0.00%
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.
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