Table 6-14 Printer Interface Signals
Pin Name (Mnemonic) CCITT / EIA Description
1 Protective ground
101/AA Connects to terminal chassis. Also connects to external ground lead of ac power cord.
2 Transmit data
103/BA From VT102:
Terminal transmits serial characters on TXD to printer. TXD held in mark state when characters are not transmitted.
3 Receive data
104/BB To VT102:
Terminal receives XON and XOFF control characters on RXD. All other characters ignored.
6 Data set ready
107/CC To VT102:
Terminal receives DTR from printer on DSR. If DTR from printer has not been on since power up or reset, terminal ignores all print requests. When DTR from printer is on, DSR indicates printer status. If DTR turns off, terminal assumes that printer cannot receive characters. If DTR turns on again, print operation completes.

NOTE: The printer's DTR has a higher priority than XON/XOFF control characters. When the printer's DTR is off, data transmission stops even if the printer interface option receives XON. When the printer's DTR goes from off to on, the terminal assumes that the XON condition is indicated.

7 Signal ground
102/AB SGND is common ground reference potential for all voltages on interface.
20 Data terminal ready
108.2/CD From VT102:
DTR is on when terminal is on. Printer usually receives DTR as DSR. Printer usually needs DTR before operation can begin.