Controller area network controller and transceiver

A Controller Area Network (CAN) transceiver comprising:

• two bus terminals for coupling said transceiver to a CAN bus;
• a transmitter arrangement configured to transmit signalling on the CAN bus via said bus terminals based on transmit data received at a transmit input, the transmit input comprising a terminal for coupling to a CAN controller, the transmitter arrangement comprising at least one transmitter configured to drive the CAN bus to a dominant state or to a recessive state based on the transmit signal, and comprising an impedance control device connected to the two bus terminals;
• a signalling detector configured to detect signalling from the controller received at the transmit input with the transmit data, the signalling detector configured to determine a length of time the transmit data comprises a logic zero state prior to a transition in the transmit data from said logic zero state to a logic one state and:
• based on the length of time being longer than a predetermined threshold, provide for control of an output impedance by the impedance control device in accordance with a first scheme comprising the controlling the output impedance to be within a predefined range of an impedance value at the dominant state while a differential driver voltage on a CAN bus connected to the CAN transceiver decreases to a predefined voltage and then increasing the output impedance over a first predetermined time duration;
• and
• based on the length of time being shorter than said predetermined threshold, provide for one of:
• control of said output impedance in accordance with a second scheme different to the first scheme;
• and no control of the output impedance by the impedance control device;
• wherein the transmitter arrangement is configured to operate at any one time in a first transmit mode or a second transmit mode, wherein in the first transmit mode the transmitter arrangement is configured to transmit said signalling with a first property and when the transmitter arrangement is in the second transmit mode the transmitter arrangement is configured to transmit said signalling with a second property, different to the first property;
• wherein, based on the length of time being longer than a predetermined threshold, as determined by the signalling detector, the transmitter arrangement is configured to operate in the first transmit mode;
• and
• wherein, based on the length of time being shorter than a predetermined threshold, as determined by the signalling detector, the transmitter arrangement is configured to operate in the second transmit mode.

A system comprising a CAN controller in combination with a CAN transceiver;

• wherein the CAN transceiver comprises:
• two bus terminals for coupling said transceiver to a CAN bus;
• a transmitter arrangement configured to transmit signalling on the CAN bus via said bus terminals based on transmit data received at a transmit input, the transmit input comprising a terminal for coupling to a CAN controller, the transmitter arrangement comprising at least one transmitter configured to drive the CAN bus to a dominant state or to a recessive state based on the transmit signal, and comprising an impedance control device connected to the two bus terminals;
• a signalling detector configured to detect signalling from the controller received at the transmit input with the transmit data, the signalling detector configured to determine a length of time the transmit data comprises a logic zero state prior to a transition in the transmit data from said logic zero state to a logic one state and:
• based on the length of time being longer than a predetermined threshold, provide for control of an output impedance by the impedance control device in accordance with a first scheme comprising the controlling the output impedance to be within a predefined range of an impedance value at the dominant state while a differential driver voltage on a CAN bus connected to the CAN transceiver decreases to a predefined voltage and then increasing the output impedance over a first predetermined time duration;
• and
• based on the length of time being shorter than said predetermined threshold, provide for one of:
• control of said output impedance in accordance with a second scheme different to the first scheme;
• and no control of the output impedance by the impedance control device;
• and
• wherein the CAN controller comprises:
• a transmit output configured to provide transmit data to the CAN transceiver for transmission on the CAN bus;
• a receive input configured to receive received data from the CAN transceiver representative of received signalling from the CAN bus;
• and
• a functionality selector configured to provide a mode signal with the transmit data that instructs the CAN transceiver to operate in a second transmit mode rather than a first transmit mode and disable operation of the impedance control device in accordance with the first scheme, wherein providing the mode signal comprises the controller being configured to provide transmit data comprising a logic zero state having a length of time less than the predetermined threshold prior to a transition in the transmit data from said logic zero state to a logic one state.

A method for operating a Controller Area Network, CAN, (CAN) transceiver, the CAN transceiver comprising two bus terminals for coupling said transceiver to a CAN bus and a transmitter arrangement configured to transmit signalling on the CAN bus via said bus terminals based on transmit data received at a transmit input, the transmit input comprising a terminal for coupling to a CAN controller, the transmitter arrangement comprising at least one transmitter configured to drive the bus to a dominant state or to a recessive state based on the transmit signal, and comprising an impedance control device connected to the two bus terminals;

• the method comprising:
• detecting, using a signalling detector, signalling from the controller received at the transmit input with the transmit data;
• determining a length of time the transmit data comprises a logic zero state prior to a transition in the transmit data from said logic zero state to a logic one state and:
• based on the length of time being longer than a predetermined threshold, providing for control of an output impedance by the impedance control device in accordance with a first scheme comprising the controlling the output impedance to be within a predefined range of an impedance value at the dominant state while a differential driver voltage on a CAN bus connected to the CAN transceiver decreases to a predefined voltage and then increasing the output impedance over a first predetermined time duration;
• and
• based on the length of time being shorter than said predetermined threshold, providing for one of:
• control of said output impedance in accordance with a second scheme different to the first scheme;
• and no control of the output impedance by the impedance control device;
• wherein the signalling detector comprises a time filter configured to provide a switching signal based on said length of time being one of longer or shorter than the predetermined threshold, wherein the signalling detector further comprises a multiplexer configured to receive said switching signal and, based on the switching signal, switch between:
• a first state in which the multiplexer is configured to connect a first control block to provide signalling to the impedance control device for provision of the first scheme;
• and
• a second state in which the multiplexer is configured to either:
• connect a second control block to provide signalling to the impedance control device for provision of the second scheme;
• or disconnect the first control block from the impedance control device.