參數(shù)資料
型號: MC68332
廠商: Motorola, Inc.
英文描述: 32-Bit Modular Microcontroller
中文描述: 32位微控制器模塊
文件頁數(shù): 79/88頁
文件大小: 446K
代理商: MC68332
MC68332
MC68332TS/D
MOTOROLA
79
6.6 SCI Submodule
The SCI submodule is used to communicate with external devices through an asynchronous serial bus.
The SCI is fully compatible with the SCI systems found on other Motorola MCUs, such as the M68HC11
and M68HC05 Families.
6.6.1 SCI Pins
There are two unidirectional pins associated with the SCI. The SCI controls the transmit data (TXD) pin
when enabled, whereas the receive data (RXD) pin remains a dedicated input pin to the SCI. TXD is
available as a general-purpose I/O pin when the SCI transmitter is disabled. When used for I/O, TXD
can be configured either as input or output, as determined by QSM register DDRQS.
The following table shows SCI pins and their functions.
6.6.2 SCI Registers
The SCI programming model includes QSM global and pin control registers, and four SCI registers.
There are two SCI control registers, one status register, and one data register. All registers can be read
or written at any time by the CPU.
Changing the value of SCI control bits during a transfer operation may disrupt operation. Before chang-
ing register values, allow the transmitter to complete the current transfer, then disable the receiver and
transmitter. Status flags in the SCSR may be cleared at any time.
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 — 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:
SCI Baud Rate = System Clock/(32SCBR)
or
SCBR = System Clock(32SCK)(Baud Rate desired)
where SCBR is in the range {1, 2, 3, ..., 8191}
Pin Names
Receive Data
Mnemonics
RXD
Mode
Function
Receiver Disabled
Receiver Enabled
Transmitter Disabled
Transmitter Enabled
Not Used
Serial Data Input to SCI
General-Purpose I/O
Serial Data Output from SCI
Transmit Data
TXD
SCCR0
— SCI Control Register 0
$YFFC08
15
14
13
12
0
0
0
0
SCBR
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
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