Audit CAN Termination Locations Before Debugging Firmware

A CAN network assembled from individually tested boards can contain too many terminators, no terminator at one end, or a long branch created by a test adapter. Firmware changes will not correct those physical conditions. Begin with a drawing of the actual wiring, including every adapter used during the failing test.

Locate the ends of the physical bus

Mark the main cable, each node connection and every branch length. Identify where termination is fitted and whether it is enabled by a jumper, switch or assembly option. The end of the main cable is a physical location, not necessarily the node called master in software.

Texas Instruments’ CAN physical-layer report describes end termination and conventional single or split implementations. Apply the topology guidance to the intended CAN physical layer and operating speed. A schematic showing one resistor on each board does not establish the correct network configuration.

Use resistance checks with defined conditions

With the network in an appropriate unpowered and discharged state, a resistance measurement across the pair can help identify missing or additional passive terminations. Two ideal 120 ohm resistors in parallel would measure 60 ohms. That simple example is a diagnostic expectation only when the rest of the connected circuitry does not materially affect the measurement.

Record where the measurement was taken and what remained connected. Split termination, protection components and other paths may influence readings or settling. Do not interpret one meter value as proof that the terminations are physically located at the correct cable ends.

Inspect stubs and service equipment

Include the branch created by an analyzer, programming harness or removable node. A network that works without the analyzer can behave differently with an additional cable attached. Check the applicable timing and topology guidance rather than assuming that low message traffic makes a long stub harmless.

Verify connector pin mapping and the intended ground or reference arrangement. The differential pair still has a common-mode operating range at each transceiver. A wiring mistake or ground difference can produce symptoms that resemble a termination problem.

Compare powered waveforms and error behavior

Observe the bus at informative locations using suitable probing. Record which node transmits, the bit timing configuration, supply conditions and error counters. Compare results after one controlled wiring correction rather than changing topology, firmware and termination simultaneously.

Document the allowed terminator settings for production and installation. If identical boards can occupy intermediate or end positions, make the configuration method unambiguous. Retain the network map with the test report so future debugging starts from the actual physical arrangement instead of an assumed two-node bench setup.