MC68HC11G5 Datasheet, PDF (91/195 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcontroller

Freescale Semiconductor, Inc.
SECTION 7
SERIAL COMMUNICATIONS INTERFACE
This section describes the UART type serial communications interface system (SCI). The SCI can
be used, for example, to connect a CRT terminal or personal computer to the MCU or to form a serial
communication network connecting several widely distributed MCUs. It should be noted that the SCI
is one of two independent serial I/O subsystems in the MC68HC11G5. The other serial I/O system
on the MC68HC11G5, the serial peripheral interface (SPI), provides for high speed synchronous
serial communication to peripherals or other MCUs (usually located on the same PC board as the
MC68HC11G5).
7.1 OVERVIEW AND FEATURES
The SCI on the MC68HC11G5 is a full duplex UART type asynchronous system. The SCI uses
standard non-return-to-zero (NRZ) format (one start bit, eight or nine data bits, and one stop bit).
An on-chip baud rate generator derives standard baud rate frequencies from the MCU oscillator.
Both the transmitter and the receiver are double buffered so back-to-back characters can be
handled easily, even if the CPU is delayed in responding to the completion of an individual character.
The SCI transmitter and receiver are functionally independent but use the same data format and
baud rate.
7.1.1 SCI Two-wire System Features:
• Standard NRZ (mark/space) format.
• Advanced error detection method includes noise detection for noise duration of up to 1/16th bit
time.
• Full-duplex operation.
• Software programmable for one of 32 different baud rates.
• Software selectable word length (eight or nine bit words).
• Separate transmitter and receiver enable bits.
• Capable of being interrupt driven.
• Four separate enable bits available for interrupt control.
7.1.2 SCI Receiver Features
• Receiver wake-up function (idle line or address bit).
• Idle line detect.
SERIAL COMMUNICATIONS INTERFACE
7-1
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