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12
12.3.3 Starting CSIO Transmission
When all of the following transmit conditions are met after you finished initialization, the serial I/O
starts transmit operation.
(1) Transmit conditions when CSIO mode internal clock is selected
• The SIO Control Register's transmit enable bit is set to 1.
• Transmit data (8 bits) is written to the lower byte of the SIO Transmit Buffer Register (transmit
buffer empty bit = 0).
(2) Transmit conditions when CSIO mode external clock is selected
• The SIO Control Register 0's transmit enable bit is set to 1.
• Transmit data is written to the lower byte of the SIO Transmit Buffer Register (transmit buffer
empty bit = 0).
• A falling edge of transmit clock on the SCLKI pin is detected.
Note 1 : While the transmit enable bit is cleared to 0, writes to the transmit buffer register are
ignored. Always be sure to set the transmit enable bit to 1 before you write to the
transmit buffer register.
Note 2 : When the internal clock is selected, a write to the lower byte of the transmit buffer
register in Note 1 above triggers a start of transmission.
Note 3 : The transmit status bit is set to 1 at the time data is set in the lower byte of the SIO
Transmit Buffer Register.
When transmission starts, the serial I/O transmits data following the procedure below.
• Transfer the content of the SIO Transmit Buffer Register to the SIO Transmit Shift Register.
• Set the transmit buffer empty bit to 1. (Note)
• Start sending data synchronously with the shift clock beginning with the LSB.
Note : A transmit buffer empty interrupt request and/or a DMA transfer request can be generated
when the transmit buffer is emptied.
12.3.4 Successive CSIO Transmission
Once data is transferred from the transmit buffer register to the transmit shift register, the next data
can be written to the transmit buffer register even when transmission of the preceding data is not
completed. When the next data is written to the transmit buffer before completion of the preceding
data transmission, the preceding and the next data are successively transmitted.
To see if data has been transferred from the transmit buffer register to the transmit shift register,
check the SIO Status Register's transmit buffer empty flag.
12.3 Transmit Operation in CSIO Mode
12-31
SERIAL I/O
Ver.0.10
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