VT100.net: Digital VT102 User Guide

Table 6-6 Full-Duplex with Modem Control (FDX B) Signals
Pin	Name (Mnemonic)	CCITT / EIA	Switch	Description
1	Protective ground (PGND)	101/AA	-	Connects to terminal chassis. Also connects to external ground through third wire of power cord.
2	Transmit data (TXD)	103/BA	S6	From VT102: When switch S6 is on (closed), TXD transmits serial characters and breaks generated by the 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 (RXD)	104/BB	-	To VT102: RXD receives serial characters from the computer.
4	Request to send (RTS)	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 (CTS)	106/CB	S2	To VT102: When switch S2 is on (closed), CTS indicates when modem is ready to transmit data. When on, modem is ready to transmit data and CTS indicator is on. When off, modem is not ready to transmit data and CTS indicator is off.
NOTE: When S2 is on (closed), switch S3 must be off (open).
6	Data set ready (DSR)	107/CC	-	To VT102: When DSR is on: DSR indicator is on Modem is connected to a communication line Modem is ready to use modem control signals. When DSR is off: DSR indicator is off Terminal performs a disconnect.
7	Signal ground (SGND)	102/AB	-	SGND is common ground reference potential for all connector signals except protective ground. SGND connects to protective ground conductor.
8	Receive line signal detector (RLSD)	109/CF	-	To VT102: Also called carrier detect, RLSD is on when communication line signals are good enough to transfer data. When off, the communication line signals are not good enough to transfer data; data received is ignored.
12	Speed indicator (SI)	112/CI	S4	To VT102: When switch S4 is on (closed), SI controls terminal transmit and receive speeds. When on, transmit and receive speeds are 1200 baud regardless of modem transmit and receive speed SET-UP feature selections. When off, transmit and receive speeds are modem transmit and receive speed SET-UP feature selections.
20	Data terminal ready (DTR)	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 disconnect. When on, the modem usually can answer calls (modem auto answer option). When off, modem usually disconnects and does not answer calls.
23	Speed select (SPSD)	111/CH	S10	From VT102: SPSD is on when receive speed SET-UP feature selection is greater than 600 baud. SPSD is off when speed is 600 baud or less.