MSC8144E Reference Manual, Rev. 3
20-6
Freescale
Semiconductor
UART
A 13-bit modulus counter in the baud-rate generator derives the baud rate for both the receiver
and the transmitter. A value ranging from 1 to 8191 is written to the SBR[12–0] bits to determine
the CLASS64 clock divisor. Writing a 0 to SBR[12–0] disables the baud-rate generator. The SBR
bits are in the SCI Baud-Rate Register (SCIBR). 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 two
sources of error:
Integer division of the CLASS64 clock may not give the exact target frequency.
Synchronization with the bus clock can cause phase shift.
Refer to Section 21.2.2, Data Sampling, for details on adjusting to the received baud rate at the
receiver.
Table 20-3 lists some examples of achieving target baud rates with a CLASS64 clock frequency
of 100 MHz, using the following formula:
20.1 Transmitter
The UART transmitter accommodates either 8-bit or 9-bit data characters. The state of the M bit
in the SCI Control Register (SCICR) determines the length of the data characters. When 9-bit
data is transmitted, bit T8 in the SCIDR is the ninth bit (bit 8).
Table 20-3. Baud Rates (CLASS64 clock = 100 MHz)
Bits SBR
Receiver Clock (Hz)
Transmitter Clock (Hz)
Target Baud Rate
Error (Percentage)
14
7,142,857
446,429
460,000
3.04
27
3,703,704
231,481
230,000
0.64
54
1,851,852
115,741
115,000
0.64
98
1,020,408
63,776
64,000
0.35
163
613,497
38,343.6
38,400
0.15
326
306,748
19,171.8
19,200
0.15
651
153,610
9600.6
9600
0.006
1302
76,804.9
4800.3
4800
0.006
2604
38,402.5
2400.15
2400
0.006
5208
19,201.2
1200.08
1200
0.006
Note:
The error relates only to the first source error.
UART baud rate
System clock
16
SCIBR 12– 0
[
]
×
(
)
⁄
=
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...