This cable connects the DE-9 (9-pin D-sub) serial port of a PC — wired as DTE per TIA/EIA-232-F — to the proprietary 15-pin female connector fitted on the internal 14.4 kbps Speedster modem. The Speedster’s 15-pin connector is not a standard DA-15 game-port fitting; it uses a non-standard pin arrangement to carry the same logical RS-232 signals found on a conventional DB-25 modem connector. Nine signals are routed across the cable: the three ground lines on the modem side (pins 1, 8, and 15) all connect to the single signal-ground pin (pin 5) of the DE-9.
9 PIN D-SUB FEMALE to the Computer
15 PIN FEMALE to the modem.
| 9 pin | 15 pin | Dir | |
|---|---|---|---|
| Carrier Detect | 1 | 11 | IN |
| Receive Data | 2 | 13 | IN |
| Transmit Data | 3 | 12 | OUT |
| Data Terminal Ready | 4 | 10 | OUT |
| System Ground | 5 | 1+8+15 | —— |
| Data Set Ready | 6 | 3 | IN |
| Request to Send | 7 | 4 | OUT |
| Clear to Send | 8 | 5 | IN |
| Ring Indicator | 9 | 6 | IN |
Signals
- DCD (Carrier Detect) — asserted by the modem (DCE) when a carrier is detected on the telephone line.
- RxD (Receive Data) — serial data received from the modem and presented to the computer.
- TxD (Transmit Data) — serial data sent from the computer to the modem.
- DTR (Data Terminal Ready) — asserted by the computer to signal readiness; the modem may disconnect the line if this drops.
- GND (System Ground) — signal ground reference; the three modem-side ground pins (1, 8, 15) are all tied to DE-9 pin 5.
- DSR (Data Set Ready) — asserted by the modem to indicate it is powered and ready.
- RTS (Request to Send) — asserted by the computer to request permission to transmit; used for hardware flow control.
- CTS (Clear to Send) — asserted by the modem in response to RTS, granting permission to transmit.
- RI (Ring Indicator) — pulsed by the modem to indicate an incoming call.
Notes
The direction column is relative to the computer (DTE): IN = signal received by the computer; OUT = signal driven by the computer.
The Speedster 15-pin connector is a proprietary interface; its pin numbering does not correspond to any published DA-15 or other standard D-sub assignment. The modem provides three separate ground contacts (pins 1, 8, and 15) which are bonded together at the DE-9 end to the single signal-ground contact (pin 5).
All signal levels follow TIA/EIA-232-F conventions: logic 1 (Mark) = −3 V to −15 V; logic 0 (Space) = +3 V to +15 V.
References
- Interface Circuits for TIA/EIA-232-F — SLLA037A — Texas Instruments application note covering TIA/EIA-232-F electrical characteristics, DE-9 and DB-25 DTE signal assignments, and DTE/DCE interface design.