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Implementing CAN/CSA-ISO/IEC 10173-01:2023: Synchronous Interface at 37.5 Mbit/s – Physical Layer and Compliance Guide
Essential technical requirements for deploying 37.5 Mbit/s synchronous interfaces in accordance with the Canadian adoption of ISO/IEC 10173-01
CAN/CSA-ISO/IEC 10173-01:2023 is the Canadian adoption of the international standard ISO/IEC 10173-01, which defines a synchronous interface operating at 37.5 Mbit/s. Intended primarily for telecommunications and data exchange applications, this standard specifies the physical layer characteristics that ensure interoperability between equipment from different vendors. This article provides a detailed technical examination of the scope, key requirements, implementation considerations, and compliance pathways for engineers and system integrators.
Scope and Field of Application
The standard applies to synchronous serial interfaces used for high‑speed data transfer over balanced metallic cabling. It covers the general architecture and physical layer specifications for point‑to‑point connections operating at a nominal bit rate of 37.5 Mbit/s. Typical applications include backbone links in telecommunication networks, high‑speed interconnection between switches, and data‑intensive industrial control systems.
Relationship to Other Standards
CAN/CSA-ISO/IEC 10173-01 is part of a family of synchronous interface standards. It aligns with the electrical characteristics defined in ITU‑T Recommendation V.11 and leverages connector specifications from ISO/IEC 10173-02 (where applicable). The standard is intended to be used in conjunction with higher‑layer protocols that rely on a synchronous physical transport layer.
Tip: When designing a system that includes a 37.5 Mbit/s synchronous link, always verify that the higher‑layer protocol stack explicitly references ISO/IEC 10173-01 or its national adoption to ensure complete physical layer compatibility.
Technical Requirements for the Physical Layer
The standard defines mandatory electrical, timing, and connector specifications. The following table summarizes the key parameters.
| Parameter | Specification | Remark |
|---|---|---|
| Nominal bit rate | 37.5 Mbit/s ± 100 ppm | Clock stability required |
| Line code | Differential Manchester (Biphase Level) | Provides clock recovery and DC balancing |
| Driver output voltage | ±2.0 V to ±5.0 V differential | Into 100 Ω termination |
| Receiver sensitivity | ±200 mV differential threshold | Includes hysteresis |
| Nominal characteristic impedance | 100 Ω ± 10% (balanced) | Twisted‑pair or twinaxial cable |
| Connector type | D‑sub 15‑pin (female on DCE) | Pin assignments defined in Annex A |
| Maximum cable length | 100 m (unrepeatered) | At full bit rate over AWG 24 twisted pair |
| Jitter tolerance | 0.4 UI peak‑to‑peak at 1 kHz | Per measurement method in Clause 7 |
Electrical Characteristics
The physical layer employs differential signaling with a nominal peak‑to‑peak voltage swing of 3.0 V across the terminating resistor. The driver is required to maintain balanced output impedance (50 Ω each leg) to minimise common‑mode radiation. Rise and fall times are controlled to 4 ns ± 1 ns to limit electromagnetic interference.
Timing and Clock Recovery
All data transitions are synchronised to a transmitted clock or embedded via the differential Manchester code. The receiving device must extract the clock from the signal using a phase‑locked loop (PLL) with a capture range of at least ±150 ppm. The standard specifies a maximum cycle‑to‑cycle jitter of 0.1 UI at the transmitter.
Warning: Using cables with characteristic impedance outside the range 90–110 Ω may cause signal reflections that degrade the eye diagram and increase bit error rate beyond the acceptable 10⁻¹² limit. Always use cables qualified to the impedance requirement.
Implementation Considerations and Testing
Successful deployment of a 37.5 Mbit/s synchronous link demands attention to signal integrity and grounding. The following subsections highlight critical aspects.
Cable Selection and Termination
Only balanced cables with a characteristic impedance of 100 Ω ± 10% at frequencies up to 50 MHz should be used. Shielded twisted pair (STP) or twinaxial cable with proper grounding at the DCE side is recommended. Both ends must have a 100 Ω termination resistor (integrated or external).
Testing and Verification
To certify conformance, perform the following tests:
- Eye diagram measurement – at the output of the driver into a 100 Ω load, the eye must open at least 60% of the unit interval (UI).
- Jitter generation – measure with a high‑bandwidth oscilloscope; the intrinsic jitter must not exceed 0.15 UI peak‑to‑peak.
- Return loss – from 1 MHz to 50 MHz, the cable plant should exhibit a return loss greater than 15 dB.
- Bit error ratio (BER) test – a PRBS‑2²³-1 pattern must result in BER ≤ 10⁻¹² over a minimum test duration of 24 hours.
Compliance Tip: Use an automated test suite that follows the test procedures described in Annex C of the standard. Many accredited laboratories accept self‑test reports if the measurement setup has been validated with a reference traceable to a national metrology institute.
Compliance and Certification
Manufacturers intending to declare compliance with CAN/CSA-ISO/IEC 10173-01 must submit their equipment to an independent testing laboratory accredited by the Standards Council of Canada (SCC). The certification process includes electrical safety inspection (CSA C22.2 No. 60950‑1 or equivalent) as well as full parametric testing of the synchronous interface.
Marking and Documentation
Compliant products must bear the CSA mark next to the standard reference. The user manual shall include a statement that the interface meets the requirements of CAN/CSA-ISO/IEC 10173-01:2023 and shall list the test results for the parameters in the table above.
Maintaining Compliance
Any modification to the physical layer design (e.g., change of driver IC, cable ferrite bead, or connector vendor) may invalidate the certification. A delta compliance test is recommended for such changes.
Important: Misapplication of the ground pin (shielding return) can create ground loops that cause excessive common‑mode emissions. The standard dedicates the shell connection to earth ground at the DCE side only – do not connect it at both ends.
Frequently Asked Questions
Q: Can CAN/CSA-ISO/IEC 10173-01 be used with a protocol other than synchronous data link?
A: The standard only defines the physical layer. It can support any higher‑layer protocol that fits within the 37.5 Mbit/s synchronous stream, such as HDLC, PPP, or a proprietary framing. The physical timing and electrical requirements remain unchanged regardless of the protocol.
A: The standard only defines the physical layer. It can support any higher‑layer protocol that fits within the 37.5 Mbit/s synchronous stream, such as HDLC, PPP, or a proprietary framing. The physical timing and electrical requirements remain unchanged regardless of the protocol.
Q: What is the maximum distance when using a repeater?
A: The standard does not directly specify repeater cascading. In practice, for each repeater the maximum segment length remains 100 m, and total end‑to‑end jitter must be budgeted accordingly. It is advisable to use active regeneration with PLL re‑clocking to maintain signal quality.
A: The standard does not directly specify repeater cascading. In practice, for each repeater the maximum segment length remains 100 m, and total end‑to‑end jitter must be budgeted accordingly. It is advisable to use active regeneration with PLL re‑clocking to maintain signal quality.
Q: Is the 37.5 Mbit/s bit rate backward‑compatible with older 2 Mbit/s interfaces?
A: No. The 37.5 Mbit/s interface uses a completely different bit rate and line coding. You need a rate‑adaptation device if you wish to connect a 2 Mbit/s stream to a 37.5 Mbit/s synchronous link.
A: No. The 37.5 Mbit/s interface uses a completely different bit rate and line coding. You need a rate‑adaptation device if you wish to connect a 2 Mbit/s stream to a 37.5 Mbit/s synchronous link.
Q: Does the standard require any specific screen coverage for the cable?
A: A minimum of 85% braid coverage or an equivalent foil screen is recommended to meet the emission limits of CISPR 22 / EN 55032. The exact requirement is part of the EMC compliance regime that must be satisfied alongside the interface standard.
A: A minimum of 85% braid coverage or an equivalent foil screen is recommended to meet the emission limits of CISPR 22 / EN 55032. The exact requirement is part of the EMC compliance regime that must be satisfied alongside the interface standard.
© 2026 – Technical Article by IEC Standards Review