Hardware manual

Rev. 3.0, 09/98, page 205 of 361
10.3 Operation
10.3.1 Overview
The SCI supports serial data transfer in two modes. In asynchronous mode each character is
synchronized individually. In synchronous mode communication is synchronized with a clock
signal.
The selection of asynchronous or synchronous mode and the communication format depend on
settings in the SMR as indicated in table 10.5. The clock source depends on the settings of the
C/A bit in the SMR and the CKE1 and CKE0 bits in the SCR as indicated in table 10.6.
(1) Asynchronous Mode: Data lengths of seven or eight bits can be selected. A parity bit or
multiprocessor bit can be added, and stop bit lengths of one or two bits can be selected. These
selections determine the communication format and character length. Framing errors (FER),
parity errors (PER) and overrun errors (ORER) can be detected in receive data, and the line-break
condition can be detected.
An internal or external clock source can be selected for the serial clock. When an internal clock
source is selected, the SCI is clocked by the on-chip baud rate generator and can output a clock
signal at the bit-rate frequency. When the external clock source is selected, the on-chip baud rate
generator is not used. The external clock frequency must be 16 times the bit rate.
(2) Synchronous Mode: The transmit data length is eight bits. Overrun errors (ORER) can be
detected in receive data.
An internal or external clock source can be selected for the serial clock. When an internal clock
source is selected, the SCI is clocked by the on-chip baud rate generator and outputs a serial clock
signal. When the external clock source is selected, the on-chip baud rate generator is not used and
the SCI operates on the input serial clock.