ISO 2110:1989

Overview

ISO 2110:1989 defines the mechanical and functional characteristics of the 25‑pole (25‑pin) DTE/DCE interface connector used in data communication. The standard specifies the connector housing, contact arrangements and contact number assignments at the interface between Data Terminal Equipment (DTE) and Data Circuit‑Terminating Equipment (DCE) or parallel automatic calling equipment. It is intended for use with voice‑band modems, public data network (PDN) facilities, telegraph signal converters and automatic calling equipment where CCITT/ITU‑T Recommendations such as V.24 and V.28 apply.

Key topics and requirements

• Connector form and pinning: Defines a 25‑pole connector for DTE (male) and DCE (female) with specific contact numbering and mating orientation to ensure intermateability.
• Contact assignments: Provides a pin assignment table mapping interchange circuits (transmit/receive data, control and signalling circuits) to contact numbers; includes a comprehensive list of interchange circuits (e.g., transmitted/received data, request to send, data set ready).
• Mechanical dimensions: Specifies critical connector and contact spacing dimensions and references IEC detailed connector specifications to ensure physical compatibility.
• Locking/latching options: Recommends a locking device (latching blocks) on the DCE housing; latching blocks accept either 4‑40 UNC threads or M3 as required by national practice.
• Shielding guidance: Connector shielding is optional; if used, metallic housings on both DTE and DCE are recommended to provide a shielded interface.
• Finger clearance and layout: Informative annex provides illustrations for maximum DTE outline and minimum DCE spacing to support equipment design and multiple‑port installations.
• Normative references: Aligns with CCITT/ITU‑T V‑series recommendations, ISO 8480 (back‑up control), IEC connector standards and X‑series PDN interfaces.

Applications and users

Who benefits from ISO 2110:1989:

• Equipment designers and hardware engineers building voice‑band modems, telegraph converters, PDN interface devices, and automatic calling/answering equipment.
• System integrators and telecommunications vendors ensuring interoperable DTE/DCE cabling and pinouts.
• Test labs and procurement teams specifying connector dimensions, pin assignments and mechanical latching/shielding requirements for internationally compatible equipment. Practical use cases include wiring interface panels, developing modem interfaces compliant with V.24/V.28 signalling, and designing rack‑mount equipment with correct port spacing and latching.

Related standards

• CCITT/ITU‑T Recommendations: V.24, V.28, V.20–V.33 family, X.20, X.24
• ISO 8480 (DTE/DCE back‑up control)
• IEC Publication 807‑2 (rectangular connector details)

ISO 2110:1989 remains a fundamental reference for physical DTE/DCE compatibility where legacy 25‑pin interfaces and V‑series signalling are used.