ASYNCHRONOUS SERIAL COMMUNICATIONS INTERFACE (SCI-A)
10.6 ASYNCHRONOUS SERIAL COMMUNICATIONS INTERFACE (SCI-A)
10.6.1 Introduction
The Asynchronous Serial Communications Inter-
face (SCI-A) offers a flexible means of full-duplex
data exchange with external equipment requiring
an industry standard NRZ asynchronous serial
data format. The SCI-A offers a very wide range of
baud rates using two baud rate generator sys-
tems.
10.6.3 General Description
The interface is externally connected to another
device by two pins (see Figure 118):
– TDO: Transmit Data Output. When the trans-
mitter is disabled, the output pin is in high im-
pedance. When the transmitter is enabled and
nothing is to be transmitted, the TDO pin is at
high level.
10.6.2 Main Features
■ Full duplex, asynchronous communications
■ NRZ standard format (Mark/Space)
■ Dual baud rate generator systems
– RDI: Receive Data Input is the serial data in-
put. Oversampling techniques are used for
data recovery by discriminating between valid
incoming data and noise.
■ Independently programmable transmit and
Through these pins, serial data is transmitted and
received as frames comprising:
receive baud rates up to 700K baud.
■ Programmable data word length (8 or 9 bits)
– An Idle Line prior to transmission or reception
– A start bit
■ Receive buffer full, Transmit buffer empty and
End of Transmission flags
■ Two receiver wake-up modes:
– Address bit (MSB)
– Idle line
– A data word (8 or 9 bits) least significant bit
first
– A Stop bit indicating that the frame is com-
plete.
■ Muting
function
for
multiprocessor
This interface uses two types of baud rate genera-
tors:
configurations
■ Separate enable bits for Transmitter and
Receiver
■ Three error detection flags:
– Overrun error
– 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.
– Noise error
– Frame 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
■ LIN Master: 13-bit LIN Synch Break generation
capability
236/426
9
STMICROELECTRONICS [ ST ]
