7721 datasheet(250/577 Pages) RENESAS

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7721 Group User’s Manual

11–47

SERIAL I/O

11.4 Clock asynchronous serial I/O (UART) mode

11.4.8 Sleep mode

This mode is used to transfer data between the specified microcomputers, which are connected by using

UARTi. The sleep mode is selected by setting the sleep select bit (bit 7 at addresses 3016, 3816) to “1” when

receiving.

In the sleep mode, receive operation is performed when the MSB (D8 when the transfer data is 9 bits

length, D7 when it is 8 bits length, D6 when it is 7 bits length) of the receive data is “1.” Receive operation

is not performed when the MSB is “0.” (The UARTi receive register’s contents are not transferred to the

UARTi receive buffer register. Additionally, the receive complete flag and error flags do not change and

a UARTi receive interrupt request does not occur.)

The following shows an usage example of the sleep mode when the transfer data is 8 bits length.

Set the same transfer data format for the master and slave microcomputers. Select the sleep mode for

the slave microcomputers.

Transmit data, which has “1” in bit 7 and the address of the slave microcomputer to be communicated

in bits 0 to 6, from the master microcomputer to all slave microcomputers.

All slave microcomputers receive data of step . (At this time, a UARTi receive interrupt request occurs.)

For all slave microcomputers, check in the interrupt routine whether bits 0 to 6 in the receive data match

their own addresses.

For the slave microcomputer of which address matches bits 0 to 6 in the receive data, terminate the

sleep mode. (Do not terminate the sleep mode for the other slave microcomputers.)

By performing steps to , “ the microcomputer which performs transfer” is specified.

Transmit data, which has “0” in bit 7, from the master microcomputer. (Only the microcomputer specified

in steps to can receive this data. The other microcomputers do not receive this data.)

By repeating step , transfer can be performed between two specific microcomputers continuously.

When communicating with another microcomputer, perform steps to in order to specify the new

slave microcomputer.

Fig. 11.4.13 Sleep mode

Master

Slave B

Slave A

Slave D

Slave C

Data is transferred between the master

microcomputer and one specific slave microcomputer

selected from multiple slave microcomputers.

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