MC68331MEH16 Freescale Semiconductor, MC68331MEH16 Datasheet - Page 65

• Manufacturer Part Number: MC68331MEH16
• Description: IC MCU 32BIT 16MHZ 132-PQFP
• Manufacturer: Freescale Semiconductor
• Series: M683xxr

Specifications of MC68331MEH16

• Core Processor: CPU32
• Core Size: 32-Bit
• Speed: 16MHz
• Connectivity: EBI/EMI, SCI, SPI, UART/USART
• Peripherals: POR, PWM, WDT
• Number Of I /o: 18
• Program Memory Type: ROMless
• Voltage - Supply (vcc/vdd): 4.5 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 132-QFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Ram Size: -
• Program Memory Size: -
• Data Converters: -

5.5.1 SCI Pins
5.5.2 SCI Registers
SCCR0 — SCI Control Register 0
Bits [15:13] — Not Implemented
SCBR — Baud Rate
MC68331TS/D
RESET:
15
0
0
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.
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.
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 is in the range {1, 2, 3, ..., 8191}
Writing a value of zero to SCBR disables the baud rate generator.
The following table lists the SCBR settings for standard and maximum baud rates using 16.78-MHz and
20.97-MHz system clocks.
14
0
0
Transmit Data
Receive Data
Pin Names
13
0
0
12
0
Freescale Semiconductor, Inc.
SCBR = System Clock(32SCK)(Baud Rate Desired)
For More Information On This Product,
0
SCI Baud Rate = System Clock/(32SCBR)
Mnemonics
0
RXD
TXD
Go to: www.freescale.com
0
Receiver Disabled
Receiver Enabled
Transmitter Disabled
Transmitter Enabled
0
0
Mode
SCBR
0
0
Not Used
Serial Data Input to SCI
General-Purpose I/O
Serial Data Output from SCI
0
Function
0
1
$YFFC08
0
0
0
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