Will work with:
- LapLink from Travelling Software
25 PIN D-SUB MALE to Computer 1
25 PIN D-SUB MALE to Computer 2
The LapLink 25-pin serial cable is a full-handshake null modem cable using DB-25 connectors as defined by TIA-232 (internationally equivalent to ITU-T V.24 and V.28). It connects two computers directly — DTE to DTE — without a modem, crossing transmit and receive lines as well as all handshake signals end-to-end. This wiring satisfies software that monitors DSR and RTS/CTS, and was the standard interconnect for Travelling Software’s LapLink and the MS-DOS INTERLNK/INTERSVR utilities.
| Name | Pin | Pin | Name |
|---|---|---|---|
| Protective Ground | 1 | 1 | Protective Ground |
| Transmit Data | 2 | 3 | Receive Data |
| Receive Data | 3 | 2 | Transmit Data |
| Request to Send | 4 | 5 | Clear to Send |
| Clear to Send | 5 | 4 | Request to Send |
| Data Set Ready | 6 | 20 | Data Terminal Ready |
| Signal Ground | 7 | 7 | Signal Ground |
| Data Terminal Ready | 20 | 6 | Data Set Ready |
Notes
Both connectors are DB-25 male (TIA-232). The cable is a DTE-to-DTE null modem; no modem or DCE device is involved. Null modem wiring is not defined by TIA-232 itself — multiple incompatible variants exist; this page documents the full-handshake variant used by LapLink. Recommended cable length is 15 m (50 ft) or 2500 pF total capacitance at rated speed per V.28.
Signals
- Protective Ground (pin 1) — chassis/shield ground, connected straight through on both sides
- Transmit Data / TxD (pin 2) — serial data output from the DTE; crossed to pin 3 (RxD) on the far end (V.24 circuit 103)
- Receive Data / RxD (pin 3) — serial data input to the DTE; crossed to pin 2 (TxD) on the far end (V.24 circuit 104)
- Request to Send / RTS (pin 4) — DTE signals readiness to transmit; crossed to pin 5 (CTS) on the far end (V.24 circuit 105)
- Clear to Send / CTS (pin 5) — DTE acknowledges permission to transmit; crossed to pin 4 (RTS) on the far end (V.24 circuit 106)
- Data Set Ready / DSR (pin 6) — ready indication; crossed to pin 20 (DTR) on the far end (V.24 circuit 107)
- Signal Ground (pin 7) — common signal reference, connected straight through
- Data Terminal Ready / DTR (pin 20) — DTE ready indication; crossed to pin 6 (DSR) on the far end (V.24 circuit 108)