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7906 Group User’s Manual Rev.2.0

11-53

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 = 9-bit length,

D7 when it is 8-bit length, D6 when it is 7-bit 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 each error flag do not change, and no

UARTi receive interrupt request occurs.)

The following shows an usage example of the sleep mode when the transfer data = 8-bit length.

➀ Be sure to set the same transfer data format for the master and slave microcomputers. Additionally, be

sure to select the sleep mode for the slave microcomputers.

➁ Then, transmit the data, of which structure is as follows, from the master microcomputer:

• Bit 7 = “1”

• Bits 6 to 0 indicate the address of the slave microcomputer to be communicated

➂ Each slave microcomputer receives the data described in step ➁. (At this time, a UARTi receive interrupt

request occurs.)

➃ Be sure to check for each slave microcomputer, in the interrupt routine, whether bits 6 to 0 of the receive

data match its own address.

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

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

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

➅ Transmit the data of which bit 7 = “0” from the master microcomputer. (Only one slave microcomputer

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

➆ By repeating step ➅, continuous transfer can be performed between two specific microcomputers. When

communicating with another slave microcomputer, perform steps ➁ to ➄ in order to specify the new

slave microcomputer.

Fig. 11.4.14 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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