MC9S12Q FREESCALE [Freescale Semiconductor, Inc], MC9S12Q Datasheet - Page 392

• Manufacturer Part Number: MC9S12Q
• Description: Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Chapter 13 Serial Communications Interface (S12SCIV2) Block Description
13.4.2
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:
Table 13-10
SCI baud rate = SCI module clock / (16 * SCIBR[12:0])
392
Integer division of the module clock may not give the exact target frequency.
Baud Rate Generation
lists some examples of achieving target baud rates with a module clock frequency of 25 MHz
SBR[12-0]
1302
2604
5208
Bits
163
326
651
41
81
Table 13-10. Baud Rates (Example: Module Clock = 25 MHz)
Clock (Hz)
609,756.1
308,642.0
153,374.2
Receiver
76,687.1
38,402.5
19,201.2
9600.6
4800.0
MC9S12Q128
Rev 1.09
Transmitter
Clock (Hz)
38,109.8
19,290.1
9585.9
4792.9
2400.2
1200.1
600.0
300.0
Target Baud
38,400
19,200
9600
4800
2400
1200
Rate
600
300
Error
(%)
.76
.47
.16
.15
.01
.01
.00
.00
Freescale Semiconductor