Kyocera FS FS-1020D Operation Manual page 82

Serial Interface (Option)
SG - Signal Ground - (Pin 7)
All signals can transmit between the printer and the host computer to send
each signal with a signal ground.
DTR - Data Terminal Ready - (Pin 20)
This output is used as a buffer nearly-full handshake line. It is held high
(above 3 volts) when the buffer can accept more data.
RS-232C Interface Voltage Levels
The voltage levels of the interface signals conform to EIA RS-232C
specifications. SPACE is from 3 volts to 15 volts. MARK is from -3 volts to
-15 volts. Voltages between -3 volts and 3 volts are undefined.
B-8