Table 6-5 Full-Duplex with Data Leads Only (FDX A) Signals
Pin Name (Mnemonic) CCITT / EIA Switch Description
1 Protective ground
101/AA - Connects to terminal chassis. Also connects to external ground through third wire of power cord.
2 Transmit data
103/BA S6 From VT102:
When switch S6 is on (closed), TXD transmits serial characters and breaks generated by terminal. TXD is in mark state when no characters are transmitted.

NOTE: When S6 is on (closed), switch S7 must be off (open).

3 Received data
104/BB - To VT102:
RXD receives serial characters from the computer.
4 Request to send
105/CA S1 From VT102:
When switch S1 is on (closed), RTS is on if terminal is on-line and off if terminal is off-line.
5 Clear to send
106/CB S2 To VT102:
When switch S2 is on (closed), CTS is only used to turn CTS indicator on or off. The on condition of CTS turns CTS indicator on; the off condition turns CTS indicator off.

NOTE: When S2 is on (closed), switch S3 must be off (open).

6 Data set ready
107/CC - To VT102:
DSR turns DSR indicator on or off. The on condition of DSR signal turns DSR indicator on; the off condition turns DSR indicator off.
7 Signal ground
102/AB - SGND is common ground reference potential for all connector signals except protective ground. SGND connects to protective ground conductor.
20 Data terminal ready
108.2/CD - From VT102:
DTR is on when the terminal is on-line and off when the terminal is off-line or performing a line disconnect. When on, the modem can usually answer calls (modem auto answer option). When off, the modem usually disconnects and does not answer calls.
23 Speed select
111/CH S10 From VT102:
SPSD is on when the receive speed SET-UP feature selection is greater than 600 baud. SPSD is off when the speed is 600 baud or less.