Operation In Asynchronous Mode - Renesas H8S Series Hardware Manual

16-bit single-chip microcomputer

Hide thumbs Also See for H8S Series:

Table of Contents

Operation in Asynchronous Mode

In asynchronous mode, characters are sent or received, each preceded by a start bit indicating the start of communication

and one or two stop bits indicating the end of communication. Serial communication is thus carried out with

synchronization established on a character-by-character basis.

Inside the SCI, the transmitter and receiver are independent units, enabling full-duplex communication. Both the

transmitter and the receiver also have a double-buffered structure, so that data can be read or written during transmission

or reception, enabling continuous data transfer.

Figure 14-2 shows the general format for asynchronous serial communication.

In asynchronous serial communication, the transmission line is usually held in the mark state (high level). The SCI

monitors the transmission line, and when it goes to the space state (low level), recognizes a start bit and starts serial

communication.

One serial communication character consists of a start bit (low level), followed by data (in LSB-first order), a parity bit

(high or low level), and finally one or two stop bits (high level).

In asynchronous mode, the SCI performs synchronization at the falling edge of the start bit in reception. The SCI samples

the data on the 8th pulse of a clock with a frequency of 16 times the length of one bit, so that the transfer data is latched at

the center of each bit.

Data Transfer Format: Table 14-10 shows the data transfer formats that can be used in asynchronous mode. Any of 12

transfer formats can be selected according to the SMR setting.

Transmit/receive data

One unit of transfer data (character or frame)

Figure 14-2 Data Format in Asynchronous Communication

(Example with 8-Bit Data, Parity, Two Stop Bits)

(mark state)

Rev.6.00 Oct.28.2004 page 489 of 1016

REJ09B0138-0600H