MC9S12KG128 Datasheet, PDF (338/600 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10 Serial Communications Interface (SCIV1)
10.4.2 Baud Rate Generation
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 SBR12–SBR0 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:
Integer division of the module clock may not give the exact target frequency.
Table 10-10 lists some examples of achieving target baud rates with a module clock frequency of 25 MHz
SCI baud rate = SCI module clock / (16 * SCIBR[12:0])
Table 10-10. Baud Rates (Example: Module Clock = 25 MHz)
Bits
SBR[12-0]
41
81
163
326
651
1302
2604
5208
Receiver
Clock (Hz)
609,756.1
308,642.0
153,374.2
76,687.1
38,402.5
19,201.2
9600.6
4800.0
Transmitter
Clock (Hz)
38,109.8
19,290.1
9585.9
4792.9
2400.2
1200.1
600.0
300.0
Target Baud
Rate
38,400
19,200
9600
4800
2400
1200
600
300
Error
(%)
.76
.47
.16
.15
.01
.01
.00
.00
MC9S12KG128 Data Sheet, Rev. 1.15
338
Freescale Semiconductor