Toshiba TMP91C815F Data Book page 179

(2) Transfer modes
The SBI0CR1<SIOM1 to SIOM0> is used to select a transmit, receive or transmit / receive mode.
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8-Bit Transmit Mode
Set a control register to a transmit mode and write transmit data to the SBI0DBR.
After the transmit data is written, set the SBI0CR1<SIOS> to "1" to start data transfer. The
transmitted data is transferred from SBI0DBR to the Shift Register and output to the SO pin in
synchronized with the serial clock, starting from the least significant bit (LSB), When the
transmission data is transferred to the Shift Register, the SBI0DBR becomes empty. An INTS2
(buffer empty) interrupt request is generated to request new data.
When the internal clock is used, the serial clock will stop and automatic-wait function will be
initiated if new data is not loaded to the data buffer register after the specified 8-bit data is
transmitted. When new transmit data is written, automatic-wait function is canceled.
When the external clock is used, data should be written to SBI0DBR before new data is shifted. The
transfer speed is determined by the maximum delay time between the time when an interrupt request
is generated and the time when data is written to SBI0DBR by the interrupt service program.
When the transmit is started, after the SBI0SR<SIOF> goes "1" output from the SO pin holds final
bit of the last data until falling edge of the SCK.
Transmitting data is ended by clearing the <SIOS> to "0" by the buffer empty interrupt service
program or setting the <SIOINH> to "1". When the <SIOS> is cleared, the transmitted mode ends
when all data is output. In order to confirm if data is surely transmitted by the program, set the
<SIOF> (bit 3 of SBI0SR) to be sensed. The SBI0SR<SIOF> is cleared to "0" when transmitting is
complete. When the <SIOINH> is set to "1", transmitting data stops. SBI0SR<SIOF> turns "0".
When an external clock is used, it is also necessary to clear SBI0SR<SIOS> to "0" before new data
is shifted; otherwise, dummy data is transmitted and operation ends.
91C815-176
TMP91C815