DTE/DCE routing
A conventional DTE-to-DCE link uses straight-through signal routing because one endpoint’s TX meets the other’s RX by definition. Two DTE endpoints commonly require a null-modem cable crossing TX/RX and, where used, handshake signals. Instruments with custom connectors may ignore convention.
| Sends but never receives | TX/RX routing, wrong endpoint role or receive ground/reference. |
|---|---|
| Works only with flow control off | RTS/CTS or DTR/DSR routing incomplete. |
| First bytes work, then stalls | Handshake, buffer or timing behavior—not necessarily protocol. |
| Three-wire cable “almost works” | Application/device may require readiness lines during longer exchanges. |
Determine, do not guess
- Confirm connector numbering and RS232 voltage levels.
- Identify signal ground and output pins safely.
- Use manuals, breakout box or passive observation to establish roles.
- Check handshake state before making permanent loops.
- Document the verified cable end-to-end.
Blindly swapping wires can connect two outputs or expose non-RS232 electronics to unsafe voltage.
Use pinout troubleshooting for measurements, traffic capture after wiring is correct and adapter analysis when a USB COM port is involved. See the serial pillar.