參數(shù)資料
型號: MC68B912B32
廠商: Motorola, Inc.
英文描述: 2.5V 100ppm/Degrees C, 50uA in SOT23-3 Series (Bandgap) Voltage Reference 3-SOT-23 -40 to 125
中文描述: 16位微控制器
文件頁數(shù): 85/128頁
文件大?。?/td> 748K
代理商: MC68B912B32
MC68HC912B32
MC68HC912B32TS/D
MOTOROLA
85
13.2.2 SCI Baud Rate Generation
The basis of the SCI baud rate generator is a 13-bit modulus counter. This counter gives the generator
the flexibility necessary to achieve a reasonable level of independence from the CPU operating frequen-
cy and still be able to produce standard baud rates with a minimal amount of error. The clock source for
the generator comes from the P Clock.
13.2.3 Register Descriptions
Control and data registers for the SCI subsystem are described below. The memory address indicated
for each register is the default address that is in use after reset. The entire 512-byte register block can
be mapped to any 2-Kbyte boundary within the standard 64-Kbyte address space.
SC0BDH and SC0BDL are considered together as a 16-bit baud rate control register.
Read any time. Write SBR[12:0] anytime. Low order byte must be written for change to take effect. Write
SBR[15:13] only in special modes. The value in SBR[12:0] determines the baud rate of the SCI. The
desired baud rate is determined by the following formula:
16
BR
×
which is equivalent to:
BR is the value written to bits SBR[12:0] to establish baud rate.
NOTE
The baud rate generator is disabled until the TE or RE bit in SC0CR2 register is set
for the first time after reset, and/or the baud rate generator is disabled when
SBR[12:0] = 0.
Table 28 Baud Rate Generation
Desired
SCI Baud Rate
110
300
600
1200
2400
4800
9600
14400
19200
38400
BR Divisor for
P = 4.0 MHz
2273
833
417
208
104
52
26
17
13
BR Divisor for
P = 8.0 MHz
4545
1667
833
417
208
104
52
35
26
13
SC0BDH
— SCI Baud Rate Control Register
$00C0
Bit 7
6
5
4
3
2
1
Bit 0
BTST
BSPL
BRLD
SBR12
SBR11
SBR10
SBR9
SBR8
High
RESET:
0
0
0
0
0
0
0
0
SC0BDL
— SCI Baud Rate Control Register
$00C1
Bit 7
6
5
4
3
2
1
Bit 0
SBR7
SBR6
SBR5
SBR4
SBR3
SBR2
SBR1
SBR0
Low
RESET:
0
0
0
0
0
1
0
0
SCI Baud Rate
---------------------
=
BR
SCI Baud Rate
16
×
----------------------------------------------------
=
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