
Serial communications interface (SCI) ST72321xx-Auto
136/243 Doc ID 13829 Rev 1
15.3 General description
The interface is externally connected to another device by two pins (see Figure 63):
● TDO: Transmit Data Output. When the transmitter 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 recovery 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
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