Communication Protocols interview questions
The buses that connect parts, and how they fail.
Interviewers rarely ask you to define anything here. They describe a symptom, a measurement, or a constraint and watch how you reason. The 6 concepts below are what a strong answer draws on, and they are exactly what this product weights up when a job posting mentions spi, i2c, uart.
What interviewers probe
- SPI
- Modes, chip select, clock polarity/phase, and multi-slave topologies.
- I2CCore
- Addressing, ACK/NACK, clock stretching, pull-up sizing, and bus lockup.
- UART
- Framing, baud tolerance, and diagnosing garbled output.
- CAN Bus
- Arbitration, differential signaling, termination, and bus-off recovery.
- Protocol DebuggingCore
- Decoding a bus on a scope or analyzer and isolating the failing transaction.
- Ethernet & High-Speed Serial
- PHY/MAC split, magnetics, link training, and what a link-down means.
Understand these first
These sit underneath communication protocols and come from other topics. If this material keeps failing to stick, the gap is usually here rather than in the topic itself.
An example question
An I2C bus on a test fixture works for hours and then stops responding entirely until the board is power-cycled. SDA is stuck low. What is happening, and how would you both recover and prevent it?
What a strong answer covers
SDA stuck low almost always means a slave is mid-byte: the master was reset or glitched partway through a read, and the slave is still driving out a bit and waiting for clocks that never come. The master, seeing a busy bus, will not start — deadlock. Recover by bit-banging up to nine clock pulses on SCL to let the slave finish its byte, then issuing a STOP condition; if the master's peripheral cannot do that, take manual GPIO control of the pins. Prevent it by running that recovery routine at init before touching the bus, by adding a bus timeout so a hung transaction aborts rather than blocking, and by checking pull-up sizing and rise times, since marginal rise time makes the glitches that cause this in the first place. If it is repeatable at a specific interval, look for a watchdog or a brownout resetting the master mid-transaction.
- Identifies a slave held mid-byte as the mechanism — Explains why the slave is driving SDA and why the master cannot start.
- Describes the clock-pulse recovery — Up to nine SCL pulses followed by a STOP, or equivalent.
- Proposes prevention, not only recovery — Init-time recovery, bus timeout, pull-up and rise-time check.
- Looks for the upstream trigger — Watchdog or brownout resetting the master mid-transaction.
How this topic gets weighted
A posting that mentions spi, i2c, uart pushes communication protocols up the curriculum, and the weighting is shown with the quote from the posting that caused it. Two candidates preparing for different roles get genuinely different plans from the same taxonomy — and because mastery is stored per concept rather than per application, what you learn here still counts on your next one.
Related topics
Practice communication protocols against a real posting
Paste the job description you are actually interviewing for. The curriculum weights this topic against everything else the role needs, and the scheduler serves the questions that close your gaps fastest.