Datasheet

ST72321Rx ST72321ARx ST72321Jx
99/193
10.6 SERIAL COMMUNICATIONS INTERFACE (SCI)
10.6.1 Introduction
The Serial Communications Interface (SCI) offers
a flexible means of full-duplex data exchange with
external equipment requiring an industry standard
NRZ asynchronous serial data format. The SCI of-
fers a very wide range of baud rates using two
baud rate generator systems.
10.6.2 Main Features
■ Full duplex, asynchronous communications
■ NRZ standard format (Mark/Space)
■ Dual baud rate generator systems
■ Independently programmable transmit and
receive baud rates up to 500K baud
■ Programmable data word length (8 or 9 bits)
■ Receive buffer full, Transmit buffer empty and
End of Transmission flags
■ Two receiver wake-up modes:
– Address bit (MSB)
– Idle line
■ Muting function for multiprocessor configurations
■ Separate enable bits for Transmitter and
Receiver
■ Four error detection flags:
– Overrun error
– Noise error
– Frame error
– Parity error
■ Five interrupt sources with flags:
– Transmit data register empty
– Transmission complete
– Receive data register full
– Idle line received
– Overrun error detected
■ Parity control:
– Transmits parity bit
– Checks parity of received data byte
■ Reduced power consumption mode
10.6.3 General Description
The interface is externally connected to another
device by two pins (see Figure 2.):
– TDO: Transmit Data Output. When the transmit-
ter and the receiver are disabled, the output pin
returns to its I/O port configuration. When the
transmitter and/or the receiver are enabled and
nothing is to be transmitted, the TDO pin is at
high level.
– RDI: Receive Data Input is the serial data input.
Oversampling techniques are used for data re-
covery by discriminating between valid incoming
data and noise.
Through these pins, serial data is transmitted and
received as frames comprising:
– An Idle Line prior to transmission or reception
– A start bit
– A data word (8 or 9 bits) least significant bit first
– A Stop bit indicating that the frame is complete
This interface uses two types of baud rate generator:
– A conventional type for commonly-used baud
rates
– An extended type with a prescaler offering a very
wide range of baud rates even with non-standard
oscillator frequencies