参数资料
型号: MC68332GCAG16
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: 32-BIT, 16 MHz, MICROCONTROLLER, PQFP144
封装: 20 X 20 MM, 1.40 MM HEIGHT, 0.50 MM PITCH, ROHS COMPLIANT, LQFP-144
文件页数: 87/109页
文件大小: 787K
代理商: MC68332GCAG16
MC68332
MOTOROLA
MC68332TS/D
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
Mnemonics
Mode
Function
Receive Data
RXD
Receiver Disabled
Receiver Enabled
Not Used
Serial Data Input to SCI
Transmit Data
TXD
Transmitter Disabled
Transmitter Enabled
General-Purpose I/O
Serial Data Output from SCI
SCCR0 — SCI Control Register 0
$YFFC08
15
14
13
12
0
SCBR
RESET:
0
1
0
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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