IBM RT Series Hardware Reference Manual page 444

Interrupt
ID Interrupt Set And Reset Functions
Register
Bit Bit Bit Priority Interrupt Interrupt Interrupt
2 1 0 Level Type Source Reset Control
0 0 0 - None None -
1 1 0 Highest
Receiver
Overrun Error Reading the Line
Line or Status Register
Status Parity Error
or
Framing Error
or
Break
Interrupt
1 0 0 Second Received
Receiver Data
Reading the
Data Available Receiver Buffer
Available Register
0 1 0 Third Trans- Transmitter Reading the II R
mitter Holding (if source of in-
Holding Register terrupt) or writing
Register
Empty
into the THR
Empty
0 0 0 Fourth Modem Clear to Send Reading the Modem
Status or Status Register
Data Set Ready
or
Ring Indicator
or
Received Line
Signal Detect
Line-Control Register (Hex XFB): The system programmer
specifies the format of the asynchronous data communications
exchange through the line control register. In addition to
controlling the format, the programmer may retrieve the contents
of the line control register for inspection. This feature simplifies
system programming and eliminates the need to store line
characteristics separately in system memory.
10 Serial/Parallel Adapter