7906 datasheet(281/531 Pages) RENESAS

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SERIAL I/O

7906 Group User’s Manual Rev.2.0

11-40

11.4 Clock asynchronous serial I/O (UART) mode

11.4.3 Method of transmission

Figure 11.4.4 shows an initial setting example for relevant registers when transmitting.

The difference depending on the transfer data length (7 bits, 8 bits, or 9 bits) is the transmit data’s length

only. When selecting a 7- or 8-bit data length, be sure to set the transmit data into the low-order byte of

the UARTi transmit buffer register. When selecting a 9-bit data length, be sure to set the transmit data into

the low-order byte and bit 0 of the high-order byte.

Transmission is started when all of the following conditions (➀ to ➂) are satisfied:

➀ Transmit data is present in the UARTi transmit buffer register (transmit buffer empty flag = “0”).

➁ Transmit is enabled (transmit enable bit = “1”).

➂ The CTSi pin’s input level is “L” (when the CTS function selected).

Note: When the CTS function is not selected, condition ➂ is ignored.

By connecting the RTSi pin (receiver side) and CTSi pin (transmitter side), the timing of transmission and

that of reception can be matched. For details, refer to section “11.4.6 Receive operation.”

When using interrupts, it is necessary to set the relevant registers to enable interrupts. For details, refer

to “CHAPTER 6. INTERRUPTS.”

Figure 11.4.5 shows writing data after transmission is started, and Figure 11.4.6 shows detection of

transmit completion.

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