A modem for communication over a power supply line between at least two devices of a vehicle, wherein the modem comprises at least the following means: - a transmitting means, which is configured to encode a digital wanted signal with a spreading code and modulate it as a DSSS signal onto a sinusoidal carrier signal and transmit a resultant bus signal to the power supply line as voltage modulation, and - a receiving means, which is configured to receive the bus signal from the power supply line and demodulate the bus signal into the baseband of the DSSS signal and decode the wanted signal from the DSSS signal using the spreading code, characterized in that a resultant bus signal is injected into the power supply line on the output side of the transmitting means, wherein the modem is being capacitively coupled to said power supply line, that a microcontroller, a quartz oscillator and analog peripherals for filtering and synchronization are provided, wherein the transmitting means and the receiving means are for the most part implemented in software-based manner on a microprocessor, wherein as an analog peripheral the transmitting means comprise a signal amplifier, in which the carrier signal modulated with the DSSS signal is amplified, and further a low-pass filter for noise suppression and elimination of electromagnetically incompatible high-frequencies, and wherein as an analog peripheral the receiving means has a bandpass filter on the input side, which bandpass filter limits the signals received by the power supply line to the frequency range, used for communication, around the carrier frequency, and further mixers (91, 92), into which the resultant signal of the bandpass filter is divided and demodulated there component-wise, and low-pass filters (72, 73), which reduce the demodulated signal to the baseband of the DSSS signal and transmit it to the microcontroller for decoding. - a transmitting means, which is configured to encode a digital wanted signal with a spreading code and modulate it as a DSSS signal onto a sinusoidal carrier signal and transmit a resultant bus signal to the power supply line as voltage modulation, and - a receiving means, which is configured to receive the bus signal from the power supply line and demodulate the bus signal into the baseband of the DSSS signal and decode the wanted signal from the DSSS signal using the spreading code, characterized in that a resultant bus signal is injected into the power supply line on the output side of the transmitting means, wherein the modem is being capacitively coupled to said power supply line, that a microcontroller, a quartz oscillator and analog peripherals for filtering and synchronization are provided, wherein the transmitting means and the receiving means are for the most part implemented in software-based manner on a microprocessor, wherein as an analog peripheral the transmitting means comprise a signal amplifier, in which the carrier signal modulated with the DSSS signal is amplified, and further a low-pass filter for noise suppression and elimination of electromagnetically incompatible high-frequencies, and wherein as an analog peripheral the receiving means has a bandpass filter on the input side, which bandpass filter limits the signals received by the power supply line to the frequency range, used for communication, around the carrier frequency, and further mixers (91, 92), into which the resultant signal of the bandpass filter is divided and demodulated there component-wise, and low-pass filters (72, 73), which reduce the demodulated signal to the baseband of the DSSS signal and transmit it to the microcontroller for decoding.