Microprocessors and Interfacing

A: The boundary is systematic versus random failure coverage. ISO 26262 assumes lockstep catches transient and permanent random faults, not design or toolchain-induced common cause failures. That gap is why diverse software, end-to-end checks, or monitoring outside the lockstep domain are still expected.

A: The hard number is bits per frame: about 128 bits once arbitration, control, CRC, and inter-frame space are counted. Eight nodes times 100 frames per second gives ~102,400 bits/s. Against 500,000 bits/s, that's just over 20%, and doubling for conservatism lands you near the mid-range where EMI retries start to matter.

A: The threshold is 60 Ω across the bus with power off. Physical layer integrity comes first: termination and shorts can damage transceivers if you energize prematurely. Adding nodes incrementally localizes faults before higher-layer traffic masks them.

A: The boundary is LIN's fixed schedule. Adding frames stretches the schedule length, directly delaying actuator updates. Electrical changes or retries don't fix a deterministic timing extension; trimming diagnostics does.

A: The number that matters is microamps. A 50 kΩ pull-up at reduced Vbat sources very little current, so induced noise can toggle the input. Crank brown-outs make that window wider, which the internal pull-up doesn't guard against.

A: The boundary is fault containment, not signal integrity alone. Small resistors cap short-circuit current and damp reflections, so a wiring fault is less likely to upset multiple channels simultaneously, aligning with ISO 26262 assumptions.

A: The key number is edge rate in V/µs. Measuring it under controlled conditions tells you whether the device is high-speed or slope-controlled, which drives EMC and bus stability decisions. Guessing or deferring risks latent faults.

A: The boundary is current margin. (3.3 − 1.2) V over 1 kΩ gives ~2 mA, comfortably below 8 mA and often enough for logic-level optocouplers. Pushing to the limit hurts reliability and violates derating practice.

A: The hard boundary is noise margin versus edge rate. Temperature weakens drivers and raises resistance, so fast edges suffer. Clock reduction or physical damping addresses the cause; software changes don't.