7470_M Datasheet, PDF (105/361 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER 740 FAMILY / 7470 SERIES

HARDWARE
1.13 Serial I/O
1.13A.2 Byte specification mode
The Serial I/O of the 7470/7471 group has the byte specification mode.
This mode permits transmitting or receiving specific one-byte data out of multiple-byte data transmitted
or received through the Serial I/O bus.
2 Byte counter (Address 00DE16)
The Byte counter is located at the same address as that of the Serial I/O counter but the Serial
I/O counter is a read-only type. So this counter is not affected by any write operation to the Byte
counter. Because the Byte counter is not provided with a reload function, re-set a value to transmit
or receive data continuously.
2 SARDY
When the SARDY signal is selected in the byte specification mode, the N channel open drain is
selected as its output type, and the SRDY pins of multiple microcomputers are connected, the SARDY
signal goes to “H” only when all the microcomputers have become ready for data transfer.
2 Operations in the byte specification mode
After setting the Serial I/O mode register, specify a byte corresponding to the clock to be used for
a Serial I/O transmit/receive in the Byte counter. Where the value written in the Byte counter is n,
a Serial I/O transmit/receive is performed by the clock of the (n + 1)-th byte.
q Start of transmit/receive operation
A transfer operation is started by writing the data (arbitrary dummy data in the half-duplex data
communication)^V1 to be transmitted to the Serial I/O register.
V1: When the external clock is selected, write data into the Serial I/O register when the synchronous
clock is at “H.” However, if the Byte counter value is a value other than “0,” writing data is
enabled even if the synchronous clock is at “L.”
q Transmit/receive operation
1Each time the synchronous clock is input in 8 cycles, the Byte counter value is decremented by 1.
2With the synchronous clock of the next 8 cycles after the Byte counter value becomes “0,” a
Serial I/O transmit/receive is performed as in the ordinary mode.^V2 After completion of the 8-bit
data output, an interrupt occurs at the rise of the last cycle of the synchronous clock, so that bit
6 of the Interrupt request register (address 00FC16) is set to “1.”
3When the Byte counter overflows, the Serial I/O transfer stops.
V 2: When the Byte counter value is a value other than 0, the output of the SOUT pin goes to “H”
at the fall of the first synchronous clock. If the N channel open drain is selected as the output
type of the SOUT pin, the output is put into a high-impedance state, so the SOUT pin can be
connected to the SOUT pin of another microcomputer.
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7470/7471/7477/7478 GROUP USER’S MANUAL