mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 259

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

8.4.3
A 13-bit modulus counter in the baud rate generator derives the baud rate for both the receiver and the
transmitter. The value from 0 to 8191 written to the SBR[12:0] bits determines the module clock divisor.
The SBR bits are in the SCI baud rate registers (SCIBDH and SCIBDL). The baud rate clock is
synchronized with the bus clock and drives the receiver. The baud rate clock divided by 16 drives the
transmitter. The receiver has an acquisition rate of 16 samples per bit time.
Baud rate generation is subject to one source of error:
Table 8-13
When IREN = 0 then,
Freescale Semiconductor
•
Integer division of the module clock may not give the exact target frequency.
SCI baud rate = SCI module clock / (16 * SCIBR[12:0])
lists some examples of achieving target baud rates with a module clock frequency of 10.2 MHz.
Baud Rate Generation
SBR[12–0]
Table 8-13. Baud Rates (Example: Module Clock = 10.2 MHz)
1062
2125
4250
5795
Bits
133
266
531
17
33
66
Clock (Hz)
600,000.0
309,090.9
154,545.5
Receiver
76,691.7
38,345.9
19,209.0
9604.5
4800.0
2400.0
1760.1
MC9S12E256 Data Sheet, Rev. 1.08
Transmitter
Clock (Hz)
37,500.0
19,318.2
9659.1
4793.2
2396.6
1200.6
600.3
300.0
150.0
110.0
Target Baud
Chapter 8 Serial Communication Interface (SCIV4)
38,400
19,200
9600
4800
2400
1200
Rate
600
300
150
110
Error
(%)
2.3
.62
.62
.14
.14
.11
.05
.00
.00
.00
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