IBM RT Series Hardware Reference Manual page 72

Output Signals
-Data Terminal Ready (-DTR), Pin 33: When low, this signal informs the modem or data set that
the NS 16450 is ready to communicate. The -DTR output signal can be set to an active low by
programming bit 0 (DTR) of the modem control register to a high level. The -DTR signal is set
high by a master reset operation. The -DTR signal is set high during loop mode operation.
Note: No connection, not used.
-Request to Send (-RTS), Pin 32: When low, this signal informs the modem or data set that the
NS16450 is ready to transmit data. The -RTS output signal can be set to an active low by
programming bit 1 (RTS) of the modem control register. The -RTS signal is set high by a master
reset operation. The -RTS signal is set high during loop mode operation.
Note: No connection, not used.
-Output 1 (-OUT 1), Pin 34: With this signal, user-designated output can be set to an active low by
programming bit 2 (-OUT 1) of the modem control register to a high level. The -OUT 1 signal is
set high by a master reset operation. The -OUT 1 signal is set high during the loop mode operation.
Note: No connection, not used.
-Output 2 (-OUT 2), Pin 31: With this signal, user-designated output can be set to an active low by
programming bit 3 (-OUT 2) of the modem control register to a high level. The -OUT 2 signal is
set high by a master reset operation. The -OUT 2 signal is set high during the loop mode operation.
Note: No connection, not used.
Chip Select Out (CSOUT), Pin 24: When high, this signal indicates that the chip has been selected
by active CSO, CS1, and -CS2 inputs. No data transfer can be initiated until the CSOUT signal is a
logic 1.
Note: No connection, not used.
Driver Disable (DDIS), Pin 23: This signal goes low whenever the processor is reading data from
the NS16450. A high-level DDIS output can be used to disable an external transceiver (if used
between the processor and NS 16450 on the D7 -DO data bus) at all times, except when the
processor is reading data.
Note: No connection, not used.
-Baudout (-BAUDOUT), Pin 15: This signal is a 16x clock signal for the transmitter section of the
NS16450. The clock rate is equal to the main reference oscillator frequency divided by the
specified divisor in the baud-generator division latches. The -Baudout may also be used for the
receiver section by tying this output to the RCLK input of the chip.
Note: This pin is tied to RCLK pin 9.
Interrupt (INTRPf), Pin 30: This signal goes high whenever anyone of the following interrupt
types has an active high condition and is enabled through the IER: receiver error flag, received data
16 5080 Peripheral Adapter