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Do not use the first I2C acknowledgement as proof that a newly inserted module is ready. Qualify the physical attachment, power sequence, buffer connection, and device initialization separately. Admit transactions only after those conditions belong to the same attachment instance, and revoke that permission immediately when the instance becomes uncertain. Applicability: the concrete connection contract…

A shared interrupt line reports that at least one connected source needs attention. It does not identify that source. Attribute the event using each device’s documented status path, preserve evidence before destructive reads, and acknowledge only the state owned by the servicing driver. A low shared wire is insufficient reason to clear every connected device….

A three-wire SPI read requires the host to stop driving the shared data conductor before the peripheral sends its response. Sending zero-valued “dummy” bytes is not equivalent to releasing the output. Qualify the device mode, controller direction switching, and board signal path together, then inspect the command-to-response handover at the target pins. Applicability: the concrete…

A responding sensor is not necessarily ready to provide a new measurement. Separate supply and reset completion, internal initialization, configuration acceptance, and conversion completion. Publish the first result only when its prerequisites belong to the current startup attempt; otherwise a successful bus read can turn a reset default or retained value into plausible telemetry. Applicability:…

A slow-looking sensor trace can be an alias of a much faster input. Establish the actual conversion cadence, identify unwanted frequencies that can reach the sampler, and test the apparent component while changing a controlled acquisition parameter. A smooth chart and a larger moving average cannot establish that the original physical signal was slow. Applicability:…

A changing ADC code can reflect a changing input, a changing reference, or both. Observe the signal and reference independently, then compare their ratio with the raw code. For a ratiometric sensor, deliberately sharing the excitation/reference relationship can cancel a common change, but only when the complete signal paths preserve that relationship. Applicability: Microchip MCP3008…

Read a sensor result using the device’s documented snapshot mechanism. A sequence of individually successful byte reads can combine different conversion generations into a value that never existed. A repeated START preserves bus transaction framing; it does not independently promise that the sensor freezes its result registers. Applicability: the concrete example is Bosch BME280 normal-mode…

Assert backpressure while enough receive capacity remains for every character that can still arrive. Prove that margin by measuring the stop request at the receiver, its arrival at the peer, and the final received character. RTS/CTS is not an instantaneous stop, and a UART FIFO’s automatic protection does not automatically protect a later software queue….

For a Microchip 24LC256, split writes at the physical page boundary, issue STOP to start internal programming, and wait for programming completion before advancing. Bus acknowledgement, readiness for another command, and verified stored data are three different observations. Write protection makes that distinction especially important. Applicability: this article selects the 24LC256 behavior documented in Microchip…