IBM RT Series Hardware Reference Manual page 71

Receiver Clock (RCLK), Pin 9: This input is the 16x baud-rate clock for the receiver section of the
chip.
Serial Input (SIN), Pin 10: Serial data input from the communications link (peripheral device,
modem, or data set).
-Clear to Send (-CTS), Pin 36: The -CTS signal is a modem control function input whose condition
can be tested by the processor by reading bit 4 (CTS) of the modem status register. Bit 0 (DCTS)
of the modem status register indicates whether the -CTS input has changed state since the previous
reading of the modem status register.
Note: This pin is permanently tied low.
-Data Set Ready (-DSR), Pin 37: The -DSR signal is a modem control function input whose
condition can be tested by the processor by reading bit 5 ( DSR) of the modem status register.
When low, this signal indicates that the modem or data set is ready to establish the communications
link and transfer data with the NS 16450. Bit 1 (DDSR) of the modem status register indicates
whether the -DSR input has changed since the previous reading of the modem status register.
Note: This pin is permanently tied low.
-Received Line Signal Detect (-RLSD), Pin 38: The -RLSD signal is a modem control function
input whose condition the processor can test by reading bit 7 (RLSD) of the modem status register.
When low, this signal indicates that the data carrier had been detected by the modem or data set.
Bit 3 (RLSD) of the modem status register indicates whether the -RLSD not input has changed
state since the previous reading of the modem status register.
Notes:
1. Received Line Signal Detect is also called Data Carrier Detect (DCD), or Carrier Detect (CD).
2. This pin is permanently tied low.
-Ring Indicator
(-RI), Pin
39: The -RI signal is a modem control function input whose condition the
processor can test by reading bit 6 (RI) of the modem status register. When low, this signal
indicates that a telephone ringing signal has been received by the modem or data set. Bit 2 (TERI)
of the modem status register indicates whether the -RI input has changed from a low to high state
since the previous reading of the modem status register.
Note: This pin is permanently tied high.
VCC, Pin 40: +5 Vdc supply.
VSS, Pin 20: Ground (0 Vdc) reference.
5080 Peripheral Adapter 15