參數(shù)資料
型號(hào): MC68CK338
廠商: Motorola, Inc.
元件分類: 32位微控制器
英文描述: Highly Integrated, Low-Power, 32-Bit Microcontroller
中文描述: 高度集成,低功耗,32位微控制器
文件頁數(shù): 73/133頁
文件大小: 798K
代理商: MC68CK338
MC68CK338
MC68CK338TS/D
MOTOROLA
73
SCCR0 contains a baud rate selection parameter. Baud rate must be set before the SCI is enabled. The
CPU can read and write this register at any time.
Bits [15:13] — Not Implemented
SCBR[12:0] — Baud Rate
SCI baud rate is programmed by writing a 13-bit value to BR. The baud rate is derived from the MCU
system clock by a modulus counter.
The SCI receiver operates asynchronously. An internal clock is necessary to synchronize with an in-
coming data stream. The SCI baud rate generator produces a receiver sampling clock with a frequency
16 times that of the expected baud rate of the incoming data. The SCI determines the position of bit
boundaries from transitions within the received waveform, and adjusts sampling points to the proper po-
sitions within the bit period. Receiver sampling rate is always 16 times the frequency of the SCI baud
rate, which is calculated as follows:
or
where SCBR[12:0] is in the range {1, 2, 3, …, 8191}
Writing a value of zero to SCBR[12:0] disables the baud rate generator.
Table 43
lists the SCBR[12:0] settings for standard and maximum baud rates using a 14.44 MHz sys-
tem clock.
SCCR0 —
SCI Control Register 0
$YFFC08
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
0
0
SCBR[12:0]
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
Table 43 SCI Baud Rates
Nominal Baud Rate
Actual Rate with
14.44 MHz Clock
64.0
110.0
300.0
600.1
1200.1
2400.3
4800.5
9601.1
18802.1
37604.2
75208.3
451250.0
SCBR[12:0] Value
64
110
300
600
1200
2400
4800
9600
19200
38400
76800
$1B8B
$1006
$05E0
$02F0
$0178
$00BC
$005E
$002F
$0018
$000C
$0006
$0001
Maximum rate
SCI Baud Rate
32
)
SCBR[12:0]
(
(
)
-----------------------------------------------
=
SCBR[12:0]
SCI Baud Rate Desired
32
×
--------------------------------------------------------------------------
=
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