Aspects of the present disclosure are directed to assessing integrity of communications circuitry. As may be implemented in accordance with one or more embodiments, a circuit node carries out a test protocol utilizing characteristics of a communication protocol to detect potential integrity issues. An initial test bit sequence is transmitted to circuit nodes connected to signal lines of a bus, by providing a test voltage across the signal lines that is less than an operating voltage potential of the bus. An ensuing state of the bus is sensed, and integrity of the bus or of circuitry connected to the bus is assessed based on the sensed state of the bus and on a state that the bus is expected to be in after transmission of the initial test bit sequence, which is used as an indication of whether all of the circuit nodes received the initial test bit sequence.