9 pin D-SUB female connector to the computer
The Speedster was a mid-1990s 14.4 kbps ISA internal modem that exposed its serial interface via a 15-pin female D-sub connector on the card’s rear bracket. A cable with a DE-9 female plug on one end and a 15-pin D-sub male plug on the other connects the modem’s bracket port to the host computer’s COM port. The signals carried are the standard RS-232 set defined by ANSI/TIA/EIA-232-F — Carrier Detect, Receive Data, Transmit Data, DTR, Ground, DSR, RTS, CTS, and Ring Indicator — with the 15-pin connector providing additional contacts for modem-specific functions including a +5 V DC input and speaker audio.
2 4 6 10 12 14
- [][][][][][][][][][][][][][][] -
1 3 5 7 8 9 11 13 15
| 9 pin | 15 pin | Dir |
|---|---|---|
| Carrier Detect | 1 | 11 |
| Receive Data | 2 | 13 |
| Transmit Data | 3 | 12 |
| Data Terminal Ready | 4 | 10 |
| System Ground | 5 | 1+8+15 |
| Data Set Ready | 6 | 3 |
| Request to Send | 7 | 4 |
| Clear to Send | 8 | 5 |
| Ring Indicator | 9 | 6 |
Notes
The 15-pin D-sub connector on the Speedster bracket carries standard RS-232 handshaking signals across pins 3–6, 10–13, with Ground distributed across pins 1, 8, and 15. Pins 2 and 7 are not mapped to standard RS-232 signals in this cable; their functions are hardware-specific to the Speedster modem. Pin 9 carries a +5 V DC input for the card, and pin 14 carries speaker audio output. The DE-9 female end connects to the host’s serial (COM) port as a standard RS-232 DTE interface per TIA/EIA-232-F.
Signals
- Carrier Detect (DCD) — indicates that the modem has detected a carrier signal on the telephone line
- Receive Data (RD) — serial data received from the modem to the host computer
- Transmit Data (TD) — serial data sent from the host computer to the modem
- Data Terminal Ready (DTR) — asserted by the host to signal readiness; controls modem connection behaviour
- System Ground — common signal ground reference, connected to three pins (1, 8, 15) on the 15-pin side
- Data Set Ready (DSR) — asserted by the modem to indicate it is powered and ready
- Request to Send (RTS) — asserted by the host to request permission to send data
- Clear to Send (CTS) — asserted by the modem to grant the host permission to transmit
- Ring Indicator (RI) — asserted by the modem when an incoming call ring is detected
- Pin 2 (15-pin) — function not publicly documented
- Pin 7 (15-pin) — function not publicly documented
- Pin 9 (15-pin) — +5 V DC input to the modem card
- Pin 14 (15-pin) — speaker audio output
References
- Low-Voltage, Single-Supply 232-Standard Interface Solutions (SLLA083A) — Texas Instruments; RS-232 signal specifications and DE-9 pin assignments