7721 datasheet(232/577 Pages) RENESAS

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SERIAL I/O

7721 Group User’s Manual

11–29

11.3 Clock synchronous serial I/O mode

11.3.6 Processing on detecting overrun error

In the clock synchronous serial I/O mode, an overrun error can be detected.

An overrun error occurs when the next data is prepared in the UARTi receive register with the receive

complete flag = “1” (data is present in the UARTi receive buffer register) and next data is transferred to

the UARTi receive buffer register, in other words, when the next data is prepared before reading out the

contents of the UARTi receive buffer register. When an overrun error occurs, the next receive data is

written into the UARTi receive buffer register, and the UARTi receive interrupt request bit is not changed.

An overrun error is detected when data is transferred from the UARTi receive register to the UARTi receive

buffer register and the overrun error flag is set to “1.” The overrun error flag is cleared to “0” by clearing

the serial I/O mode select bits to “0002” or clearing the receive enable bit to “0.”

When an overrun error occurs during reception, initialize the overrun error flag and the UARTi receive

buffer register before performing reception again. When it is necessary to perform retransmission owing to

an overrun error which occurs in the receiver side, set the UARTi transmit buffer register again before

starting transmission again.

The method of initializing the UARTi receive buffer register and that of setting the UARTi transmit buffer

(1)

Method of initializing UARTi receive buffer register

Clear the receive enable bit to “0” (Reception disabled).

Set the receive enable bit to “1” again (Reception enabled).

(2)

Method of setting UARTi transmit buffer register again

Clear the serial I/O mode select bits to “0002” (Serial I/O invalid).

Set the serial I/O mode select bits to “0012” again.

Set the transmit enable bit to “1” (Transmission enabled), and set the transmit data to the UARTi

transmit buffer register.

7721 Datasheet(PDF) 232 Page - Renesas Technology Corp