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CHAPTER 13 UART
Table 13.4-3 Description of the Serial Status and Data Register (SSD)
Bit name
Description
bit7
RDRF: Received
data flag bit
This bit indicates the state of serial input data register (SIDR).
When this bit is 1, reading the SSD register, then the SIDR register clears
RDRF.
When this bit and reception interrupt request bit (RIE) are 1, the reception
interrupt request is output.
This bit is intended only for read. Writing a value into this bit has no
significance and does not affect any operation.
bit6
ORFE: Over-run/
Framing error flag bit
This bit indicates that the over-run or framing error occurs.
When an error occurs (ORFE = 1), no data is transferred from the
reception shift register to the SIDR register. Therefore, when an error
occurs, the RDRF bit is not set. When this bit is 1, reading the SSD
register then SIDR register clears the ORFE bit with 0.
When this bit and reception interrupt request bit (RIE) are 1, the reception
interrupt request is output.
This bit is intended only for read. Writing a value into this bit has no
significance and does not affect any operation.
bit5
TDRE: Transmitted
data flag bit
This bit indicates the state of serial output data register (SODR).
When this bit is 1, reading the SSD register and writing data into the
SODR register outputs the data to the serial data output terminal (UO).
When this bit and transmission interrupt request bit (TIE) are 1, the
transmission interrupt request is output.
bit4
TIE: Transmission
interrupt request
enable bit
This bit enables or disables the transmission interrupt request to the CPU.
When this bit and transmission data flag bit (TDRE) are 1, the
transmission interrupt request is output.
bit3
RIE: Reception
interrupt request
enable bit
This bit enables or disables the reception interrupt request to the CPU.
When this bit and reception data flag bit (RDRF) are 1, the reception
interrupt request is output.
When this bit and error flag bit (ORFE) are 1, the reception interrupt
request for an error is output.
bit2
Unused bit
The value read out from this bit is undefined.
Writing a value into this bit does not affect any operations.
bit1
TD8/TP: Bit-8
transmitting data/
parity bit
When parity is not used and operating mode is 2 or 3 (the length of data
to be transmitted/received is 9), this bit is handled as bit 8 in the SODR
register. When operating mode is not 2 or 3 and parity is not used, this bit
is not significant.
When parity is used, this bit selects even parity or odd parity for the
transmitted data.
bit0
RD8/RP: Bit-8
receiving data/parity
bit
When parity is not used and operating mode is 2 or 3 (the length of data
to be transmitted/received is 9), this bit is handled as bit 8 in the SIDR
register. When operating mode is not 2 or 3 and parity is not used, this bit
is not significant.
When parity is used, this bit indicates the parity of received data.