MPC563XM Reference Manual, Rev. 1
1238
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
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.
The baud rate generator is enabled when the TE bit or RE bit in the
SCI Control Register 2 (SCICR2)
is
set to 1 for the first time. The baud rate generator is disabled when SBR = 0.
Baud rate generation is subject to one source of error:
•
Integer division of the module clock may not give the exact required target baud rate.
lists some examples of achieving target baud rates with a module clock frequency of
MCLK = 10.2 MHz.
27.4.3.1
Module Clock
The module clock MCLK is derived from the system bus clock. It has the same phase and frequency.
27.4.3.2
Transmitter Clock
The transmitter clock TCLK is used to drive the data to the serial bus via the TXD pin. It is derived from
the system bus clock by the baud rate generator. The baud rate generator is controlled by the value of the
SBR[12:0] field in the
SCI Baud Rate Register High (SCIBDH)
. The frequency of the transmitter clock is determined by
of the transmitted bits, which is denoted as the
bit time
.
Eqn. 27-1
27.4.3.3
Receiver Clock
The receiver clock RCLK is used to sample the data received on the RXD or TXD pin. It is derived from
the system bus clock by the baud rate generator. The baud rate generator is controlled by the value of the
Table 27-29. Baud Rates Error Example (MCLK = 10.2 MHz)
SBR[12:0]
RCLK (Hz)
TCLK (Hz)
Target Baud Rate
Error (%)
17
600,000.0
37,500.0
38,400
2.3
33
309,090.9
19,318.2
19,200
.62
66
154,545.5
9659.1
9600
.62
133
76,691.7
4793.2
4800
.14
266
38,345.9
2396.6
2400
.14
531
19,209.0
1200.6
1200
.11
1062
9604.5
600.3
600
.05
2125
4800.0
300.0
300
.00
4250
2400.0
150.0
150
.00
5795
1760.1
110.0
110
.00
f
TCLK
f
MCLK
16 SBR 12:0
[
]
⋅
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=