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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.