D-37
SYSTEM REGISTER QUICK REFERENCE
D.34 LSRn
Serial Line Status
LSR0, LSR1
(read only) Expanded Addr:
ISA Addr:
Reset State:
LSR0 LSR1
F4FDH F8FDH
03FDH 02FDH
60H 60H
7 0
— TE TBE BI FE PE OE RBF
Bit
Number Bit
Mnemonic Function
7 — Reserved. This bit is undefined.
6 TE Transmitter Empty:
The transmitter sets th is bit to indicate that the transmit shift register an d
transmit buffer register are both empty. Writing to the transmit buffer
register clears this bit.
5 TBE Transmit Buffer Empty:
The transmitter sets this bit aft er it transfers data from the tra nsmit buffer
to the transmit shift regi ster. Writing to the transmit buffe r register clears
this bit.
4 BI Break Interrupt:
The receiver sets this bit whenever the received data input is held in the
spacing (logic 0) state for longer than a full word transmission time.
Reading the receive buffer register or the serial line sta tus register clears
this bit.
3 FE Framing Error
The receiver sets this bit to indicate that the received character did not
have a valid stop bit. Reading the receive buffer register or the serial l ine
status register clears this bit. If data frame is set for two stop bits the
second stop bit is ignored.
2 PE Parity Error:
The receiver sets this bit to indicate that the received data character did
not have the correct parity. Reading the receive bu ffer register or the
serial line status register clears this bit.
1 OE Overrun Error:
The receiver sets this bit to indicate an overrun error. An overrun occurs
when the receiver transfers a received character to the receive buffer
register before the CPU reads the buffer’s old character. Reading the
serial line status register clears this bit.
0 RBF Receive Buffer Full:
The receiver sets this bit after it transfers a received character from the
receive shift register to the receive buffer register. Reading the receive
buffer register clears thi s bi t.