MC68HC912B32MFU8 MOTOROLA [Motorola, Inc], MC68HC912B32MFU8 Datasheet - Page 85

• Manufacturer Part Number: MC68HC912B32MFU8
• Description: 16-Bit Microcontroller
• Manufacturer: MOTOROLA [Motorola, Inc]

13.2.2 SCI Baud Rate Generation
13.2.3 Register Descriptions
SC0BDH — SCI Baud Rate Control Register
SC0BDL — SCI Baud Rate Control Register
MC68HC912B32
MC68HC912B32TS/D
RESET:
RESET:
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.
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:
which is equivalent to:
BR is the value written to bits SBR[12:0] to establish baud rate.
SCI Baud Rate
BR
=
---------------------------------------------------- -
16 SCI Baud Rate
BTST
SBR7
Bit 7
Bit 7
0
0
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.
MCLK
=
-------------------- -
16 BR
MCLK
SBR6
BSPL
6
0
6
0
SCI Baud Rate
Desired
BRLD
SBR5
14400
19200
38400
1200
2400
4800
9600
110
300
600
Table 28 Baud Rate Generation
5
0
5
0
SBR12
SBR4
BR Divisor for
4
0
4
0
P = 4.0 MHz
NOTE
2273
833
417
208
104
52
26
17
13
—
SBR11
SBR3
3
0
3
0
BR Divisor for
P = 8.0 MHz
SBR10
4545
1667
SBR2
833
417
208
104
52
35
26
13
2
0
2
1
SBR9
SBR1
1
0
1
0
SBR8
SBR0
Bit 0
Bit 0
0
0
MOTOROLA
High
Low
$00C0
$00C1
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