Microcontroller Selection Questions and Answers

Answer: A

Only the real code, compiled with the real settings and running from the real memory, exercises the wait states and cache behaviour that decide the answer. Benchmarks and scaling arguments are useful for shortlisting and unreliable for committing.

Answer: B

A part that cannot be bought is not a candidate, and forty weeks against a six month schedule is decisive. Availability belongs in the first screen alongside the peripheral set, as many designers learned during the shortages.

Answer: C

Most small parts have no external memory bus at all, so running out means changing the device, and that is exactly why the headroom is bought at the start. A part with an external bus can be extended and needs less internal margin.

Answer: D

The price gap has indeed narrowed, but the smallest 8-bit parts still win on cost, on package size and often on sleep current, and for a thermostat those are the criteria that matter. Always is the word that makes the assertion false.

Answer: A

Correct answer: the guaranteed minimum flash endurance in write cycles

Endurance is a specified, guaranteed parameter that bears directly on whether the part can serve the application - a device logging to flash every minute needs a very different figure from one programmed once. Transistor count, foundry and wafer diameter are facts about how the part is made and predict nothing about how it will perform.

Answer: B

Five million records over the decade against a hundred thousand erases means each sector must serve fifty times its rating unless the writes are spread. Spreading them across many sectors, and packing many records into each erase, is what wear levelling does.

Answer: C

A mode that saves a microampere but takes ten milliseconds and a full re-initialisation to leave is a loss for anything waking every second. The energy per wake-sleep cycle, not the static current, is what has to be compared.

Answer: D

One fewer device and its passives is a real saving in board area and assembly, but the regulator's characteristics are then fixed and its quiescent current cannot be chosen. Decoupling is needed either way and the temperature grade is unaffected.

Answer: A

Two years later nobody remembers why the part was chosen, and the matrix is what prevents the same investigation being repeated or a constraint being forgotten in a redesign. It is cheap to write and expensive to omit.

Answer: B

A hundred thousand hours is 4167 days, a little over eleven years. Whether that is enough depends on the product's service life, and the calculation is worth doing before a design commits to writing a log entry every hour.