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8XC196NP, 80C196NU USER’S MANUAL
The receiver checks for a valid stop bit. Unless a stop bit is found within the appropriate time, the
framing error (FE) bit in the SP_STATUS register is set. When the stop bit is detected, the data
in the receive shift register is loaded into SBUF_RX and the receive interrupt (RI) flag is set. If
this happens before the previous byte in SBUF_RX is read, the overrun error (OE) bit is set.
SBUF_RX always contains the latest byte received; it is never a combination of the last two bytes.
SP_STATUS
Address:
Reset State:
1FB9H
0BH
The serial port status (SP_STATUS) register contains bits that indicate the status of the serial port.
7 0
RPE/RB8 RI TI FE TXE OE — —
Bit
Number
Bit
Mnemonic
Function
7 RPE/RB8 Received Parity Error/Received Bit 8
RPE is set if parity is disabled (SP_CON.2 = 0) and the ninth data bit
received is high.
RB8 is set if parity is enabled (SP_CON.2 = 1) and a parity error
occurred.
Reading SP_STATUS clears this bit.
6 RI Receive Interrupt
This bit is set when the last data bit is sampled. Reading SP_STATUS
clears this bit.
This bit need not be clear for the serial port to receive data.
5 TI Transmit Interrupt
This bit is set at the beginning of the stop bit transmission. Reading
SP_STATUS clears this bit.
4 FE Framing Error
This bit is set if a stop bit is not found within the appropriate period of
time. Reading SP_STATUS clears this bit.
3 TXE SBUF_TX Empty
This bit is set if the transmit buffer is empty and ready to accept up to two
bytes. It is cleared when a byte is written to SBUF_TX.
2 OE Overrun Error
This bit is set if data in the receive shift register is loaded into SBUF_RX
before the previous bit is read. Reading SP_STATUS clears this bit.
1:0 — Reserved. These bits are undefined.
Figure 8-8. Serial Port Status (SP_STATUS) Register