ISO 4902:1989

Overview

ISO 4902:1989 - Information technology: Data communication - 37-pole DTE/DCE interface connector and contact number assignments - specifies the mechanical and electrical contact assignments for the data terminal equipment (DTE) / data circuit-terminating equipment (DCE) interface where CCITT Recommendations V.24 together with V.10 and V.11 apply. The standard defines the 37‑pole connector (and references 9‑pin usage in scope), contact numbering, connector housing dimensions, optional shielding, and recommended latching (locking) provisions to ensure intermateability between DTE and DCE equipment.

Key topics and requirements

• Connector type and dimensions: Detailed drawings and dimensions for the 37‑pole connector housing, male and female contacts, and contact spacing to ensure mechanical intermateability.
• Contact numbering and pairing: Assignment tables map contact numbers to interchange circuits (e.g., 102 - signal ground, 103 - transmitted data, 104 - received data). Contact 1 is reserved for shield continuity; paired contacts (e.g., 2 & 20, 3 & 21) align with multipair cabling.
• Electrical interface context: Applies where CCITT/ITU‑T V.24 is used with V.10 (unbalanced) and V.11 (balanced) signalling; annexes provide guidance for interworking mixed V.10/V.11 and V.28 configurations.
• Locking and shielding: DCE connector uses two latching blocks (M3 threaded holes); DTE may use screws or latching levers. Connector shielding is optional but, if fitted, must be implemented on both DTE and DCE housings.
• Informative annexes: Annex A (finger clearance and outline guidance), Annex B (generator/receiver interconnecting configurations), Annex C (interworking guidance with V.28 and ISO 2110). Annexes are informative and support design decisions.

Practical applications and users

ISO 4902 is essential for:

• Telecommunications and modem manufacturers designing DTE/DCE interfaces compatible with V.24/V.10/V.11 signalling.
• Hardware engineers and connector manufacturers producing compliant 37‑pole connectors, cable adaptors, and latching/shielding accessories.
• System integrators and test labs ensuring interoperability of modems, data sets and terminal equipment across national installations.
• Standards and compliance teams verifying pin assignments and grounding practices (note guidance on shield grounding and avoidance of ground loops).

Practical use cases include modem interfaces, data communication equipment racks, multi‑section shielded cabling, and retrofit adapters between equipment using different CCITT signalling types.

Related standards

• ISO 2110 (25‑pin DTE/DCE interface)
• ISO 4903 (75‑pin DTE/DCE interface)
• CCITT/ITU‑T: V.10, V.11, V.24, V.28, V.36, V.37 and related signalling recommendations
• IEC Publication 807‑2 (connector specifications)

Keywords: ISO 4902:1989, 37‑pole connector, DTE/DCE interface, pin assignments, CCITT V.24, V.10, V.11, connector shielding, latching block, pin numbering.