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Chapter 11 Serial Interface 0, 1
Operation
Activation Factor for Communication
At transmission, if any data is written to the transmission data buffer TXBUFn, a start condition is gener-
ated to start transfer. At reception, if a start condition is received, communication is started. At reception,
if the data length of "L" for start bit is longer than 0.5 bit, that can be regarded as a start condition.
Transmission
Data transfer is automatically started by writing data to the transmission data buffer TXBUFn. When the
transmission has completed, the serial 0 transmission interrupt SCnTIRQ is generated.
Reception
Once a start condition is received, reception is started after the transfer bit counter that counts transfer
bit is cleared. When the reception is completed, the serial n reception interrupt SCnRIRQ is generated.
Duplex communication
Duplex communication, that the transmission and reception can be operated independently at the same
time is available. On duplex communication, the frame mode and parity bit of the used data on transmis-
sion / reception should have the same polarity.
Transfer Bit Count Setup
The transfer bit count is automatically set after the frame mode is specified by the SCnFM1 to 0 flag of
the SCnMD2 register. If the SCnCMD flag of the SCnMD1 register is set to "1", and UART communica-
tion is selected, the setup by the synchronous serial data transfer bit count selection flag SCnLNG2 to 0
is no more valid.
Data Input Pin Setup
The communication mode can be selected from with 2 channels (data output pin (TXD pin), data input
pin (RXD pin)), or with 1 channel (data I/O pin TXD pin). The RXD pin can be used only for serial data
input. The TXD pin can be used for serial data input or output. The SCnIOM flag of the SCnMD1 register
can specify which pin, RXD or TXD to input the serial data. "Data input from TXD pin" is selected to be
with 1 channel communication, transmission / reception is switched by controlling TXD pin's direction by
the PnDIR0 flag of the PnDIR register. At that time, the RXD pin can be used as a general port.
Received Buffer Empty Flag
When the communication complete interrupt SCnRIRQ is generated, data is stored to RXBUFn from the
internal shift register, automatically. If data is stored to the shift register RXBUFn, the recieved buffer
empty flag SCnREMP of the SCnMD3 register is set to "1". This indicates that the reception data is going
to be read. SCnREMP is cleared to "0" by reading data in RXBUFn.