Serial Communications Interface (SCI)

The SCI is a universal asynchronous receiver transmitter (UART), one of two independent serial I/O subsystems in the MC68HC11E9. It has a standard non return to zero(NRZ) format (one start, eight or nine data, and one stop bit). Several baud rates are available. The SCI transmitter and receiver are independent, but use the same data format and bit rate.

The serial data format requires the following conditions:

• An idle-line in high state before transmission or reception.
• A start bit, logic zero, transmitted or received, that indicates the start of each character.
• Data that is transmitted and received least significant bit(LSB) first.
• A stop bit, logic one, used to indicate the end of a frame. (A frame consists of a start bit, a character of eight or nine data bits, and a stop bit.)
• A break (defined as the transmission or reception of a logic zero for some multiple number of frames).

Selection of the word length is controlled by the M bit of SCI control register SCCR1.

• Transmit Operation
• Receive Operation
• SCI Registers