Microprocessors and Interfacing

A: The hard boundary is the watchdog window itself: as long as service occurs between the min and max tick counts, the watchdog is blind. A control loop oscillating at a high but legal rate can still command torque or current beyond system limits. Clock failure and brown-out are caught by separate monitors, and invalid fetches typically violate execution timing before the window opens.

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.