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CHAPTER 13
SERIAL INTERFACE SIO0
User’s Manual U12790EJ2V0UD
(9) Transfer start
Serial transfer is started by setting transfer data to serial I/O shift register 0 (SIO0) when the following two
conditions are satisfied.
Serial interface SIO0 operation control bit (CSIE0) = 1
Internal serial clock is stopped or SCK0 is at high level after 8-bit serial transfer.
Cautions 1. If CSIE0 is set to “1” after data is written to SIO0, transfer does not start.
2. Because the N-ch open-drain output must be made high impedance for data reception,
write FFH to SIO0 in advance.
However, when the wakeup function specification bit (WUP) = 1, the N-ch open-drain
output is always made high impedance. Thus, it is not necessary to write FFH to SIO0.
3. If data is written to SIO0 when the slave is busy, the data is not lost.
When the busy state is cleared and the SB0 (or SB1) input is set to the high level (READY)
state, transfer starts.
Upon termination of 8-bit transfer, serial transfer automatically stops and the interrupt request flag (CSIIF0)
is set.
Be sure to set the pins used to input/output data after input of the RESET signal and before serial transfer
of 1 byte as follows.
<1> Set the output latches of P25 and P26 to 1.
<2> Set bit 0 (RELT) of serial bus interface control register 0 (SBIC0) to 1.
<3> Clear the output latches of P25 and P26, which were set to 1 above, to 0.