Patent Description:
CAN networks provide communication between nodes over a bus. Nodes that are connected to the bus can transmit to and receive data from other nodes that are connected to the bus. A CAN network implements the CAN protocol for defining the communication between the nodes.

<CIT> relates to a transceiver applied to a node having a sleep/wakeup function.

A Controller Area Network, CAN, typically comprises a plurality of nodes each connected to a two wire CAN bus. The nodes can communicate with each other by sending and receiving signalling to and from the CAN bus.

<FIG> shows an example node <NUM>. The node includes a CAN controller <NUM>, such as a microcontroller. The CAN controller <NUM> may have the CAN protocol embedded therein, such as in a controller module. The CAN controller <NUM> provides and receives signalling from the CAN bus <NUM> using a CAN transceiver <NUM>. The CAN transceiver <NUM> therefore typically provides signalling to the CAN bus based on transmit data received from the CAN controller <NUM> and provides data to the CAN controller <NUM> based on signalling it receives from the CAN bus <NUM>. The CAN transceiver <NUM> may be configured to provide the signalling to the CAN bus <NUM> with the appropriate voltage levels for logic high and logic low based on the transmit data and with the appropriate differential signalling for the two-wire CAN bus according to the CAN protocol.

Reference to a CAN transceiver or a CAN controller herein may be understood as a controller and transceiver that implements, at least in part, the CAN protocol in full or in part or the CAN FD protocol in full or in part. The functionality described for the CAN transceiver or CAN controller herein may comprise increased functionality above what is currently defined in the CAN protocol.

The CAN controller <NUM> is configured to provide transmit data at a transmit output <NUM> for receipt at a transmit input <NUM> of the CAN transceiver <NUM>. The transmit output <NUM> and transmit input <NUM> may comprise integrated circuit pins. Thus, the transmit input pin <NUM> is configured to receive transmit data from the CAN controller <NUM>. The CAN transceiver <NUM> is configured to receive signalling from the CAN bus <NUM> and provide received data based on the signalling to a receive output <NUM> for receipt at a receive input <NUM> at the CAN controller <NUM>. The receive output <NUM> and the receive input <NUM> may comprise integrated circuit pins.

The CAN transceiver <NUM> comprises a transmitter arrangement <NUM> configured to transmit signalling on the CAN bus <NUM> based on said transmit data. The CAN transceiver <NUM> also comprises a receiver arrangement <NUM> configured to receive signalling from the CAN bus <NUM> and provide received data based on the signalling.

The transmitter arrangement <NUM> comprises at least one transmitter and, in this example comprises two transmitters <NUM>, <NUM>. The at least one transmitter is configured to operate in a first transmission mode or a second transmission mode, wherein in the first transmission mode the transmitter arrangement is configured to transmit said signalling with a first property and wherein in the second transmission mode the transmitter arrangement is configured to transmit said signalling with a second property. The first and second property may comprise one or more property types, such as baud rate (e.g. maximum, minimum or average baud rate), voltage level scheme, encoding scheme or other. However, for ease of explanation herein, the first and second property may comprise baud rate such that the first property comprises a first baud rate and the second property comprises a second baud rate wherein the first baud rate is higher than the second baud rate. The use of a higher baud rate may improve the rate with which data can be transmitted on the CAN bus. Nevertheless, it will be appreciated that the first and second property could (in any of the example embodiments herein) alternatively be, or additionally be, a voltage level scheme used to represent logic <NUM> and logic <NUM> on the CAN bus <NUM>.

Therefore, going forward and as an example only, the first transmission mode will be referred to as the fast transmission mode and the second transmission mode will be referred to as the slow transmission mode.

The receiver arrangement <NUM> comprises at least one receiver and, in this example comprises two receivers <NUM>, <NUM>. The at least one receiver may be configured to operate in a first receive mode or a second receive mode, wherein in the first receive mode the receiver arrangement <NUM> is configured to receive signalling from the bus <NUM> with the first property and in the second receive mode the receiver arrangement <NUM> is configured to receive signalling from the bus <NUM> with the second property. As described above, the property may any one or more of baud rate, voltage level scheme, encoding scheme or other.

Therefore, going forward and as an example only, the first receive mode will be referred to as the fast receive mode and the second receive mode will be referred to as the slow receive mode.

As mentioned above and as shown in this example, the transmitter arrangement <NUM> comprises a first transmitter <NUM> configured to transmit signalling at said higher baud rate and a second transmitter <NUM> configured to transmit signalling at a lower baud rate. In one or more examples, the first transmitter <NUM> is configured to transmit said signalling with a first voltage level scheme to represent logic high and logic low on the CAN bus <NUM> and the second transmitter <NUM> is configured to transmit said signalling with a second voltage level scheme to represent logic high and logic low different to the first voltage level scheme. Thus, the first and second transmitters <NUM>, <NUM> may differ in terms of one or more of the baud rate they are capable of transmitting, the voltage level scheme used for the signalling applied to the CAN bus and a slew rate at which the transmitter can transition between logic high and logic low voltage levels (to provide said signalling with the first property and the second property). Each of the transmitters <NUM>, <NUM> has two outputs to provide signalling to the two wire CAN bus <NUM>.

It will be appreciated that in one or more examples, the transmitter arrangement <NUM> may comprise one transmitter and one or more of a change in voltage applied thereto, a bias voltage and the switching in or out of additional circuitry may be used to enable the provision of the fast transmission mode and slow transmission mode by the single transmitter. In other examples, more than two transmitters may be used to provide the fast transmission mode and the slow transmission mode.

As mentioned above and as shown in this example, the receiver arrangement <NUM> comprises a first receiver <NUM> configured to receive signalling at said higher baud rate and a second receiver <NUM> configured to receive signalling at the lower baud rate. In one or more examples, the first receiver <NUM> is configured to receive said signalling with a first voltage level scheme to determine logic high and logic low of the signalling from the CAN bus <NUM> and the second receiver <NUM> is configured to receive said signalling with a second voltage level scheme to determine logic high and logic low from the signalling from the CAN bus <NUM> different to the first voltage level scheme. Thus, the first and second receivers <NUM>, <NUM> may differ in terms of one or more of the baud rate they are capable of receiving in terms of distinguishing between symbols on the CAN bus <NUM> and the voltage level scheme used for the signalling on the CAN bus (to enable the receipt of signalling with the first and second property). Each of the receivers <NUM>, <NUM> has two inputs to receive signalling from the two wire CAN bus <NUM> and a single output to provide for onward transmission of the received data to the CAN controller <NUM> or any other components therebetween.

It will be appreciated that in one or more examples, the receiver arrangement <NUM> may comprise one receiver and one or more of a change in voltage applied thereto, a bias voltage and the switching in or out of additional circuitry may be used to enable the provision of the fast receive mode and slow receive mode by the single receiver. In other examples, more than two receivers may be used to provide the fast receive mode and slow receiver mode.

The determination of whether it is required for the node <NUM> to operate in the fast transmission mode rather than the slow transmission mode may be made by the CAN controller <NUM>. However, in one or more examples, it may be necessary to reliably and robustly signal this requirement to the CAN transceiver <NUM> and in such a way that the transmitter arrangement <NUM> of the CAN transceiver <NUM> can reliably and robustly transition between the fast transmission mode and slow transmission mode and vice-versa and, when required, the receiver arrangement <NUM> can transition between the slow receive mode and fast receive mode and vice-versa.

In the present examples, this "mode" signalling is provided by using a particular encoding scheme on the transmit data that is passed from the CAN controller <NUM> to the CAN transceiver <NUM>. Thus, for the CAN controller, when the fast transmission or fast receive mode is required, the particular encoding scheme is applied to the transmit data and it may be passed to the CAN transceiver <NUM> via the transmit output <NUM> and transmit input <NUM>. Once the particular encoding scheme is detected by the CAN transceiver <NUM> it can provide the appropriate mode for the time the transmit data is encoded by said encoding scheme. When the particular encoding scheme is not present or a different encoding scheme is used, the CAN transceiver <NUM> may, such as by default, adopt the other of the slow/fast transmission/receive modes. It will be appreciated that in other examples, the determination of the first line code encoding of the transmit data may signify the use of the slow transmission mode or slow receive mode.

In particular, in this and one or more examples, the transmitter arrangement <NUM> is configured to operate in the fast transmission mode based on a determination that the transmit data is encoded with a first line code and configured to operate in the slow transmission mode based on a determination that the transmit data is not encoded with the first line code. The transceiver <NUM> also includes a decoder <NUM> to remove the "mode signalling" first line encoding of the transmit data. The decoder <NUM> is configured to decode the first line code of the transmit data and provide the decoded transmit data to the transmitter arrangement <NUM> to provide for said transmission of the signalling on the CAN bus at least when the transmitter arrangement is in the fast mode (or the slow transmission mode if the encoding is intended to indicate use of the slow transmission mode). Depending on the signalling required on the CAN bus, the decoder and the need to decode the first line code "mode signalling" for the transmitter arrangement may not be necessary in some examples.

In one or more examples, the decoder <NUM> is coupled to the transmit input <NUM> by connection <NUM> to receive the transmit signal and is coupled to the first transmitter <NUM> to provide its decoded output. More generally, it may be coupled to the transmitter arrangement <NUM> and configured to provide the decoded transmit data when the transmit data is received in the form encoded by the first line code whereas when the transmit data is received in the form not encoded by the first line code, the decoder <NUM> does not provide the transmit data to the receiver arrangement (or it does provide it but it is ignored by the receiver arrangement). Thus, the transmitter arrangement <NUM> may be configured to receive the transmit data that bypasses the decoder when the first line code is not used to encode the transmit data. In this example, the second transmitter <NUM> receives the transmit data directly from the transmit input <NUM> by connection <NUM>. The decoder <NUM> may also provide a clock output representative of the clock used to encode the transmit data with the first line code at output <NUM>. The ability to derive a clock signal may be useful for the transceiver.

In one or more examples, it may be desirable for the CAN transceiver <NUM> to effectively distinguish between the transmit data that is encoded with the first line code compared to the transmit data when it is not encoded with the first line code. In one or more examples, the first line code comprises a code in which the first line coded transmit data has shorter pulse widths than said transmit data that is not encoded with the first line code. Thus, the first line code may be such that the maximum pulse width possible i.e. the time between edges (of logic high and logic low or two or more other levels) in a stream of transmit data is less (or more) when the transmit data is encoded with the first line code than the minimum (or maximum) pulse width when it is not used. The determination of the pulse width may use minimum pulse width detected, maximum pulse width or average pulse width over a plurality of pulses or the pulse with of one pulse (e.g. high-low-high or low-high-low transition of the signalling, e.g., differential signalling). Thus, the temporal length of the pulse widths of the transmit data compared to a threshold time may provide one way of determining if the first line code is applied to the transmit data or not. It will be appreciated that other determining factors could be used such as number of edges detected in a particular time relative to a threshold or the number of voltage levels used in the encoding among others.

In one or more examples, the first line code comprises a code that uses the phase to encode the transmit data. In one or more examples, the first line code comprises one of Manchester code; Return-to-Zero, RZ, code; and differential Manchester code. In the description that follows the first line code is a phase code and, in particular, Manchester encoding is applied to the transmit data by the CAN controller <NUM> and detected by the CAN transceiver <NUM>. In one or more examples, phase encoding may inherently reduce pulse widths making the application of the phase encoding detectable by the CAN transceiver by measuring pulse width time.

Thus, in one or more examples, for the period of time in which the transmit data is encoded with the first line code, the transceiver operates in the fast transmission mode excluding any mode-change-time required to detect the presence or absence of first line code encoded transmit data, and, for the period of time in which the transmit data is not encoded with the first line code, the transceiver operates in the slow transmission mode excluding any mode-change-time required to detect the presence or absence of the first line code encoded transmit data. The use of different encoding of the transmit data to signal the desired transmission mode for the transceiver may provide a reliable signalling method because the signalling of the desired mode is continuously present rather than being signalled in a one-off manner by way of a "mode change message".

It will be appreciated that in one or more examples, the use of the phase encoding may be used to indicate use of the slow transmission mode rather than the fast transmission mode. Provided that the encoding or non-encoding of the transmit data using a particular code can be distinguished by the CAN transceiver <NUM> it can be used to signify the transmission mode and/or receive mode that should be adopted.

In one or more examples, the CAN transceiver <NUM> comprises a mode detector <NUM> configured to determine the presence or absence of the first line code encoding of the transmit data and provide a mode-switch signal to the transmitter arrangement <NUM> to select either the fast transmission mode or the slow transmission mode. The mode detector may be coupled to receive the transmit data from the transmit input <NUM>, such as by connection <NUM>. The mode detector <NUM> may therefore be continually checking for the presence or absence of the first line code encoding to control the mode-switch-signal. The mode-switch signal may comprise a plurality of signals that may be provided to the relevant components in the CAN transceiver <NUM>. In this example and any other example, the mode switch signal may comprise an enable/disable signal provided to the first transmitter <NUM> by connection <NUM>. Further, the mode switch signal may comprise an enable/disable signal provided to the second transmitter <NUM> by connection <NUM>. Thus, in the fast transmission mode, the first transmitter <NUM> may be enabled and the second transmitter <NUM> may be disabled. Likewise, in the slow transmission mode, the first transmitter <NUM> may be disabled and the second transmitter <NUM> may be enabled.

A similar enabling and disabling of the first receiver <NUM> and the second receiver <NUM> may be provided by the mode detector <NUM>. However, in this example, the enable/disable signal applied to the second transmitter <NUM> is used to control a switch <NUM>. The switch <NUM> is configured to select which one of the first and second receivers <NUM>, <NUM> is connected to the receive output <NUM> at any one time. Thus, each of the first and second receivers <NUM>,<NUM> will receive the signalling from the CAN bus <NUM> but only one will be able to provide received data based on said signalling to the receive output <NUM> for receipt by the CAN controller <NUM>. In one or more examples, when the mode detector <NUM> enables the second transmitter <NUM>, the switch <NUM> connects the second receiver <NUM> to the receive output <NUM> whereas when the mode detector disables the second transmitter <NUM>, the switch <NUM> connects the first receiver <NUM> to the receive output <NUM>. It will be appreciated that, and as will be described later, the mode detector <NUM> may be configured to enable one or none of the first and second transmitters. In one or more examples, the mode detector may be configured to enable only one of the receivers <NUM>, <NUM> or, in other examples, none of the receivers depending on the requirements of the CAN controller <NUM>.

The mode detector <NUM> may have a default configuration in which the slow transmission mode and/or slow receive mode is selected and the fast transmission mode and fast receive mode is not selected. Thus, use of a slow transmission mode and slow receive mode may be the default at start-up and/or on occurrence of an error and/or on occurrence of a reset event.

Turning now to the example physical configuration of the CAN controller <NUM>, the CAN controller <NUM> may comprise a controller module <NUM> configured to output the transmit data at <NUM>. The transmit data may be provided to the transmit output <NUM> for the CAN transceiver (in this example via switch <NUM>). An encoder <NUM> also receives the transmit data output by the controller module <NUM> and encodes it using the first line code. The encoder <NUM> may receive a clock input at <NUM> for use in the encoding. The encoded transmit data is output at <NUM> to a second switched terminal of the switch <NUM>.

The CAN controller <NUM> comprises a mode selector configured to provide a controller mode signal, e.g. fast mode signal, that instructs the CAN transceiver to operate in a fast transmission mode rather than a slow transmission mode. As discussed above in relation to the operation of the CAN transceiver <NUM>, the CAN controller is configured such that the controller mode signal provides for the encoding of the transmit data with a first line code by the encoder <NUM> which, in turn, instructs the CAN transceiver <NUM> to operate in the fast transmission mode (in this example). The controller <NUM> is configured such that the absence of the controller mode signal or the provision of a different controller mode signal provides for the non-encoding of the transmit data with the first line code, which, in turn, instructs the CAN transceiver <NUM> to operate in the slow transmission mode (in this example). Thus, the mode selector in this example is provided by the controller module <NUM> being configured to output a controller mode signal at <NUM> to control the position of the switch <NUM>. The switch <NUM> has two positions; one in which the transmit data as output by the controller module is coupled to the transmit output <NUM> without being encoded by the first line code and a second in which the transmit data as output by the encoder <NUM> is coupled to the transmit output <NUM>. Thus, the controller mode signal of the mode selector determines whether the encoded transmit data, encoded by the encoder <NUM>, is provided to the CAN transceiver or whether the transmit data that bypasses the encoder <NUM> is provided to the CAN transceiver. It will be appreciated that the transmit data output by the controller module <NUM> takes an encoded form, which may be non-return-to-zero, NRZ, encoded or other form. Thus, the transmit data not encoded by the encoder <NUM> may comprise NRZ encoded transmit data and the transmit data encoded by the encoder <NUM> may comprise NRZ encoded transmit data that is further encoded with a phase code, such as Manchester encoding. The decoder <NUM> of the CAN transceiver <NUM> may therefore remove the phase code thereby returning the transmit data to the NRZ encoded form. The controller module <NUM> also receives the received data from the receive input <NUM>.

Turning to example <FIG>, an example first line code is shown comprising Manchester encoding. The encoding clock is shown at <NUM> which is provided to the encoder <NUM> at input <NUM>. The transmit data from output <NUM> is shown at <NUM>. The transmit data shown at <NUM> may comprise transmit data that is intended to be transmitted on the CAN bus by the CAN transceiver in the fast transmission mode. The transmit data encoded by the Manchester encoding is shown at <NUM>. Thus, a logic <NUM> in the transmit data is encoded as a rising edge in the middle of the clock period. A logic <NUM> in the transmit data is encoded as a falling edge in the middle of the clock period. No data is encoded at the edges located between clock periods as these edges are used to ensure the encoder is in the correct state to represent the next logic value with an appropriate rising or falling edge.

The decoder <NUM> of the CAN transceiver <NUM> may be configured to extract the clock signal from the encoded transmit data as shown at <NUM>. The decoder <NUM> uses the rising and falling edges to decode the transmit data and provides the output as shown at <NUM>.

The properties of the Manchester code is that the pulse width has a minimum length <NUM> of half the clock period and a maximum length <NUM> of a clock period <NUM>.

The clock signal at <NUM> for the encoder <NUM> should be synchronous with the clock signal of the controller module <NUM> that generates the data stream that forms the transmit data. Thus, the phase encoding will be applied in synchrony with the logic states of the data stream of transmit data. In one or more examples, the clock signal <NUM> has the same or faster clock frequency compared to the symbol frequency of the data stream of transmit data.

For example, to support 10Mbps during the transmission of the transmit data the clock frequency at <NUM> for the encoder <NUM> may be <NUM> (10Mbps means a bit time of 100ns which requires a clock period time of 100ns and therefore a clock frequency of <NUM>). Thus, at 10Mbps with a repeating data pattern of <NUM>. , the Manchester coding provides a transmit signal having a base band frequency of <NUM>, hence the use of a twice as fast phase encode frequency clock. The clock for a typical CAN controller <NUM> may already be higher than <NUM> for supporting 10Mbps, and the clock frequency may be <NUM> for example. This means the clock at <NUM> for the encoder <NUM> can be easy derived/divided from the clock typically used by the controller module <NUM>. It will be appreciated that the absolute frequencies mentioned are just practical examples and the concept is functional with other frequencies.

Example <FIG> shows an example mode diagram of the CAN transceiver <NUM> and it will be described how the modes of the CAN transceiver <NUM> control the fast and slow transmission modes of the transmitter arrangement <NUM> and the fast and slow receive modes of the receive arrangement <NUM>.

In summary, in these examples, the CAN transceiver <NUM> is configured to determine whether or not the transmit data is encoded by the first line code by measuring the pulse width of the transmit data and, if the pulse width is below a threshold time, the transmitter arrangement is configured operate in the fast transmission mode and, if the pulse width is above the threshold time, the transmitter arrangement is configured operate in the slow transmission mode.

Thus, the CAN transceiver <NUM> has a slow mode <NUM> in which the transmitter arrangement <NUM> is placed in or defaults to the slow transmission mode. In the slow mode <NUM> the receiver arrangement <NUM> may also be placed in or default to the slow receive mode. The CAN transceiver <NUM> may also have a fast-TX mode <NUM> in which the transmitter arrangement is placed in the fast transmission mode. In the fast-TX mode <NUM> the receiver arrangement may also be placed in or default to the fast receive mode. The CAN transceiver <NUM> may also have a Fast-RX mode in which the node <NUM> does not transmit but is configured to receive signalling at the higher baud rate from the CAN bus <NUM>. In the fast-RX mode, the transmitter arrangement <NUM> may be disabled. Thus, both the first transmitter <NUM> and the second transmitter <NUM> may be provided with a mode signal that disables them or the disabled state may be one or both of their default states and no mode signal may be provided to them. In the fast-RX mode, the receiver arrangement <NUM> is placed in the fast receive mode.

We will now describe how the mode detector <NUM> may make the determination of which mode the transmitter arrangement <NUM> and the receiver arrangement <NUM> should be in, or, which mode the CAN transceiver <NUM> should be in which will then define which of the fast and slow modes of the transmitter arrangement <NUM> and the receiver arrangement <NUM> is used.

In one or more examples, the mode detector <NUM> is configured to determine a logic-low time and a logic-high time (shown as tTXDPIN_HIGH and tTXDPIN_LOW respectively in <FIG>).

The logic-low time comprises the length of time the transmit data was logic low since the last logic high and the logic-high-time comprises the length of time the transmit data was logic high since the last logic low. Thus, the mode detector may include a timer or other means to measure the length of time the transmit signal is or was logic low in the most recent continuous logic low state and to measure the length of time the transmit signal is or was logic high in the most recent continuous logic high state, assuming a two state signal. In other examples, further logic times may be measured.

The mode detector <NUM> is configured to, based on the logic-low-time being longer than a first time threshold (shown as tMAX in <FIG>) and the logic-high-time being shorter than a second time threshold (shown as tMIN in <FIG>), provide the mode-switch signal to the transmitter arrangement to select the fast transmission mode. This may be provided by the CAN transceiver <NUM> transitioning by transition <NUM> from slow mode <NUM> to Fast-TX mode <NUM>.

The mode detector <NUM> may be further configured to, based on the logic-low-time being longer than the first time threshold, tMAX, and/or the logic-high-time being longer than the first time threshold, tMAX, provide the mode-switch signal to the transmitter arrangement to select the slow transmission mode. This may be provided by the CAN transceiver <NUM> transitioning by transition <NUM> from the Fast-TX mode <NUM> to the slow mode <NUM>.

The second time threshold tMIN may be less than that first time threshold tMAX. In one or more examples, the first time threshold is based on the longest pulse width possible that is representative of a single logic value in the transmit data when the first line code is used. In particular, it may comprise the longest pulse width possible that is representative of a single logic value in the transmit data using the first line code plus a tolerance time tTOL. Considering the Manchester encoded transmit signal of the example, the longest pulse width is provided based on a single logic value within transmit data comprising "<NUM>. " and therefore for 10Mbps transmit data, the longest pulse width is 100ns (and the shortest is 50ns). The first time threshold tMAX may therefore comprise 100ns plus a tolerance time to account for any unintended variation in timings. The tolerance in this example may comprise <NUM>% and therefore 10ns, although other tolerances may be used. Accordingly, the first time threshold tMAX may therefore comprise 110ns in this example.

In one or more examples, the second time threshold is based on the longest pulse width possible that is representative of a single logic value in the transmit data when the first line code is used. In particular, it may comprise the longest pulse width possible that is representative of a single logic value in the transmit data using the first line code minus a tolerance time tTOL. Considering the Manchester encoded transmit signal of the example, the longest pulse width is provided based on a single logic value within transmit data comprising "<NUM>. " and therefore for 10Mbps transmit data, the longest pulse width is 100ns (and the shortest is 50ns). The second time threshold tMIN may therefore comprise 100ns minus a tolerance time to account for any unintended variation in timings. The tolerance in this example may comprise <NUM>% and therefore 10ns, although other tolerances may be used. Accordingly, the second time threshold tMIN may therefore comprise 90ns.

It will be appreciated that the tolerance times TTOL used for determination of the first and second time thresholds TMIN and tMAX may or may not be the same tolerance time tTOL. Further the tolerance may be any value between <NUM>% and <NUM>% or more of the longest pulse width time. In this example, the time thresholds are chosen based on the shortest and/or longest pulse widths when the transmit data is encoded and/or the shortest and/or longest pulse widths when the transmit data is not encoded with the first line code. It will be appreciated that by longest and shortest pulse widths, as above, we refer to the time between a first transition between logic high and logic low (in either direction) and a second transition between logic high and logic low, in the opposite direction to the first transition, wherein the time between the first and second transitions encodes a single logic value.

In Fast-TX mode <NUM>, the receiver arrangement <NUM> may be placed in a fast receive state corresponding to the fast transmission state. Given in the example of <FIG>, that the mode-switch signal used to enable and disable the second transmitter is also configured to control switch <NUM>, a corresponding receive mode may be provided without any additional mode-switch signals.

We now consider the example transitions between the slow mode <NUM> and the fast-RX mode <NUM> of <FIG>. Here, the mode detector <NUM> may be configured to provide the mode-switch signal to the receiver arrangement <NUM> to select either a fast receive mode in which the receiver arrangement is configured to receive signalling at said higher baud rate, and a slow receive mode in which the receiver arrangement <NUM> is configured to receive signalling at a lower baud rate, lower than the higher baud rate. In the fast receive mode the mode-switch signal to the transmitter arrangement <NUM> may be configured to disable the transmitter arrangement <NUM>, i.e. both the first and second transmitter.

As explained above, the mode detector is configured to determine the logic-low-time and the logic-high-time. The mode detector <NUM> is configured to, based on the logic-high-time TTXDPIN_HIGH being longer than the first time threshold tMAX and the logic-low-time tTXDPIN_LOW being less than the second time threshold tMIN, provide the mode-switch signal to the receiver arrangement <NUM> to select the fast receive mode and, optionally, provide the mode-switch signal to the transmitter arrangement to disable the transmitter arrangement. This may be provided by the CAN transceiver <NUM> transitioning by transition <NUM> from slow mode <NUM> to Fast-RX mode <NUM>.

Further, the mode detector <NUM> is configured to, based on the logic-low-time tTXDPIN_LOW being longer than the first time threshold tMAX and/or the logic-high-time tTXDPIN_HIGH being longer than the first time threshold tMAX, provide the mode-switch signal to the transmitter arrangement <NUM> to select the slow transmission mode and, optionally, the slow receive mode. This may be provided by the CAN transceiver <NUM> transitioning by transition <NUM> from Fast-RX mode <NUM> to the slow mode <NUM>.

It will be appreciated that the slow mode <NUM> may be a default mode and the absence of the conditions required for transitions <NUM> and <NUM> may result in the CAN transceiver transitioning back to the slow mode <NUM> via transitions <NUM> and <NUM>.

In summary, based on the comparison of the logic-low-time and the logic-high-time, the mode-switch signal(s) provided by the mode detector <NUM> is configured to, in the fast transmission mode or fast-TX mode <NUM>, enable the first transmitter <NUM> and disable the second transmitter <NUM>, and, in the slow transmission mode, disable the first transmitter <NUM> and enable the second transmitter <NUM>.

Further and in summary, based on the comparison of the logic-low-time and the logic-high-time, the mode-switch signal(s) provided by the mode detector <NUM> is configured to, in the fast transmission mode, enable the first receiver <NUM> and disable the second receiver <NUM> in the provision of the received data to the receive output, and, in the slow transmission mode, enable the second receiver <NUM> and disable the first receiver <NUM> in the provision of the received data to the receive output.

Further and in summary, based on the comparison of the logic-low-time and the logic-high-time, the mode-switch signal(s) provided by the mode detector <NUM> is configured to, in the fast receive mode or fast-RX mode <NUM>, enable the first receiver <NUM> and disable the second receiver <NUM> in the provision of the received data to the receive output (by the position of switch <NUM> or otherwise), and, in the slow receive mode, enable the second receiver <NUM> and disable the first receiver in the provision of the received data to the receive output (by the position of switch <NUM> or otherwise).

In one or more examples, the default state for the CAN transceiver after power-on is the slow mode <NUM>. The determination of whether a CAN controller <NUM> and CAN transceiver <NUM> is in a transmitting state or a receiving state is determined by the CAN protocol during an arbitration phase. The transmit data may be driven to a particular value at a particular time to indicate the node <NUM> "won" the arbitration phase and therefore has the right to transmit and, if the node "lost" the arbitration phase, the transmit data may be driven to an alternate particular value at the particular time. This property may be used by the mode detector <NUM> to determine whether to transition to the Fast-TX mode <NUM> or the Fast-RX mode <NUM>.

If the logic-high-time was longer compared to the first time threshold then this is detected as recessive, indicative of arbitration being lost. If the logic-low-time was shorter compared to the second time threshold then this is detected as meaning the transmit data is being phase encoded (encoded with the first line code). This prompts the state change from slow mode <NUM> to fast-RX mode <NUM>.

If the logic-low-time was longer compared to the first time threshold then this is detected as dominant, indicative of the arbitration being won. If the logic-high-time was shorter compared to the second time threshold then this is detected as meaning the transmit data is being phase encoded (encoded with the first line code). This prompts the state change from slow mode <NUM> to fast-TX mode <NUM>.

If the logic-low-time or the logic-high-time is longer compared to the first time threshold tMAX then this is indicative of the transmit data no longer being phase encoded (i.e. encoded with the first line code). This prompts the the state change to slow mode <NUM> from either the fast-RX mode <NUM> or the fast-TX mode <NUM>.

The decoder <NUM> in the CAN transceiver <NUM> will derive a clock from the Manchester encoded transmit data. This clock output will have the same accuracy as the clock used inside the controller module <NUM> and encoder <NUM> to encode the transmit data. While this extracted clock is optional for this disclosure, it can be beneficial when an accurate clock is required in the CAN transceiver <NUM> for other functionality not disclosed herein.

We now consider the timing diagrams of <FIG>. The first line <NUM> shows the output from the CAN controller module <NUM> at output <NUM> when the transmit data is generated prior to any first line code encoding that may or may not be applied. The second line <NUM> shows controller mode signal output at <NUM> that controls whether the CAN transceiver receives the example Manchester encoded transmit data or the non-Manchester encoded transmit data. The third line <NUM> shows the transmit data as received by the CAN transceiver <NUM> and therefore the first line code encoding may or may not be applied. The fourth line <NUM> shows a component part of the mode-switch signals and in particular the enable/disable signal applied to the first (fast) transmitter <NUM>. The fifth line <NUM> shows a component part of the mode-switch signals and in particular the enable/disable signal applied to the second (slow) transmitter <NUM>. The sixth line <NUM> shows the decoded transmit data received by the first (fast) transmitter <NUM> as output by decoder <NUM>. The seventh line <NUM> shows the differential signal applied to the CAN bus <NUM> comprising a CANH signal applied to one of the two wires minus the a CANL signal applied to the other of the two wires as will be familiar to those skilled in the art. The eighth line <NUM> shows the received data provided by the receiver arrangement <NUM> at the receive output <NUM> (and therefore received by the CAN controller <NUM>).

To aid explanation, the diagram of <FIG> shows the state of the various signals during the end of an arbitration phase <NUM> of the CAN protocol which is designated by a transition bit <NUM>. The arbitration phase comprises a part of the protocol where the node entitled to transmit for the upcoming transmission period is determined. After the transition bit <NUM> there is a data phase <NUM> in which the current node <NUM> transmits at a higher baud rate. The end of the data phase <NUM> is designated by a further transition bit <NUM> followed by a acknowledge phase <NUM> (which may take the same form as the arbitration phase <NUM>). Such phases will be understood by those skilled in the art of the CAN protocol. The arbitration and acknowledge phases and the transition bits are performed at a slower baud rate unless otherwise specified.

In this example timing diagram, the slower baud-rate used in arbitration is 1Mbps (although other, e.g. slower, rates may be used as will be understood by those skilled in the art of the CAN protocol) and the data-phase baud-rate is 10Mbps and the first line code, Manchester code clock is <NUM>. This means the slow data bit <NUM> and the transition bit <NUM> is <NUM> long. A fast data bit <NUM> is 100ns long and a phase encoded bit <NUM> of the transmit data at line <NUM> can be minimum 50ns and maximum 100ns long depending of the logic level sequence of the transmit data in line <NUM>. As in the example described above the first time threshold tMAX =110ns and the second time threshold tMIN=90ns.

The CAN controller module <NUM> and the CAN transceiver <NUM> start in slow mode. The transmit data of the controller module <NUM> is directed to the transmit output <NUM> via the switch <NUM> bypassing the encoder <NUM> when the controller mode signal at <NUM> is logical <NUM> as shown by the line <NUM> when it is logical <NUM> and the similarity between lines <NUM> and <NUM> during this time. The mode detector <NUM> in the transceiver <NUM> is in the slow mode and therefore the second, slow transmitter <NUM> is enabled as shown in line <NUM> being logical <NUM>, which represents the signal at <NUM>. The first, fast transmitter <NUM> is disabled in the slow mode and the line <NUM>, representing the mode-switch signal output at <NUM> is logical <NUM>. The output of the second, slow receiver <NUM> is directed to the receive output <NUM> via the switch <NUM> because the component of the mode switch signal at <NUM> is logical <NUM>. During the arbitration phase <NUM> and the beginning of the transition bit <NUM> the node may be operating as a traditional CAN node.

As mentioned above, after the arbitration phase <NUM> and before the data-phase <NUM> a dedicated transition bit <NUM> may be defined in the CAN protocol frame and it is during this time the mode change is executed to switch from the slow mode to the fast-TX or fast-RX mode that uses the higher baud rate. The switching to the higher baud rate means that the CAN controller <NUM> can now output transmit data at a higher rate and the CAN transceiver needs to switch to the appropriate mode to apply this higher rate transmit data to the CAN bus <NUM>. At time <NUM>, the CAN controller module <NUM> sets the mode signal at <NUM> to logical <NUM> as shown in line <NUM> and the switch <NUM> therefore directs the output of the encoder <NUM> to the transmit output <NUM> and therefore the transmit input <NUM>. Since the transition bit is a logical <NUM> (dominant) in line <NUM> at this time, the Manchester encoded transmit data from the encoder <NUM> becomes a pulse train with a pulse width of 50ns (determined by the <NUM> phase encoder clock), as shown in line <NUM> beginning at time <NUM>. In this example, the controller module <NUM> is configured to begin the change to the fast mode at time <NUM> because it in the middle of the transition bit <NUM>, meaning the transmit data at <NUM> as shown in line <NUM> was already logical <NUM> for 500ns (up until time <NUM>). The first high pulse <NUM> on the line <NUM> is 50ns and this means the conditions are valid for a mode change from slow mode <NUM> to fast-TX <NUM> (see transition <NUM> in <FIG>) in the CAN transceiver <NUM>. It will be appreciated that the transition may not be at the middle but other parts of the transition bit. In one or more examples, it may be advantageous for the module <NUM> to switch to the fast mode such that at least two pulses or at least four edges of encoded data are provided to the CAN transceiver <NUM> before the end of the transition bit <NUM>. As will be explained below, this may be useful to enable the decoder <NUM> to lock on to the clock used to encode the transmit data by encoder <NUM>. It will be appreciated that in other examples, such a clock lock-on process may not be required.

Before the phase decoder <NUM> in the CAN transceiver <NUM> can decode the encoded transmit data it needs to derive the clock from the transmit data stream and in this example, this happens on the "preamble" (comprising toggling data at clock rate) between time <NUM> and <NUM>. At time <NUM> the decoder <NUM> is locked on the clock and the transmit data output by the decoder <NUM> is now valid. The mode decoder <NUM> provides the mode switch signals as shown in lines <NUM> and <NUM> to enable the first, fast transmitter <NUM> and disable the second, slow transmitter <NUM>. The use of the first transmitter means the CAN bus <NUM> changes from using "dominant" and "recessive" CAN protocol voltage levels to a second voltage level scheme. Thus, prior to the data phase, the voltage level scheme shown on the CAN bus in line <NUM> is between <NUM> and <NUM> Volts, whereas when the first fast transmitter <NUM> is driving the CAN bus, the voltage level scheme comprises between -<NUM> Volts and +<NUM> Volts. Other voltage level schemes may be used. The use of the fast transmission mode and the second voltage scheme may be considered as an extension to the CAN protocol. The mode switch signals also connect the first, fast receiver <NUM> to the receive output via the switch <NUM>. The CAN transceiver <NUM> is now in fast-TX mode <NUM> with the transmitter arrangement <NUM> in fast transmission mode and the receiver arrangement <NUM> in fast receive mode.

The total length of the preamble (starting halfway through the transition bit <NUM> between times <NUM> and <NUM>) is in this example half of the transition bit (500ns) resulting in <NUM> edge transitions. This may be very robust and provide enough time for the decoder <NUM> to derive a clock from the transmit data and provide enough short (encoded with the first line code pulses) to be detected by the mode decoder <NUM>. It will be appreciated that even if the mode detector <NUM> misses the timing of one or two of the short 50ns pulses between time <NUM> and time <NUM>, this will only result in a small delay for the mode detector <NUM>.

Between time <NUM> and <NUM> the second, slow transmitter <NUM> is still enabled and tries to follow the short pulses of 50ns in the encoded transmit data. Typically, the slow transmitter <NUM> was not designed to operate that fast and the output on the CAN bus cannot be predicted also resulting in unknow data <NUM> being received by the controller <NUM>. However, this may not a problem since all the controllers <NUM> or controller modules <NUM> are typically synchronised on the CAN network they can be configured to ignore received data during the transition bit <NUM>. Thus, the controller <NUM> may be configured to ignore at least variations in the received data during a transition bit <NUM>.

During the data phase <NUM>, the higher baud rate transmit data output at <NUM> is encoded by the encoder <NUM> and the encoded transmit data is passed to the CAN transceiver <NUM>. The encoding is detected as present by the mode detector <NUM> and thus the first, fast transmitter <NUM> is maintained as enabled and can therefore transmit signalling representative of the transmit data, as decoded by decoder <NUM>, on the CAN bus <NUM>.

At the end of the data-phase <NUM> there is also a dedicated transition bit <NUM> during time <NUM>. It will be appreciated that the transition bit, in any of the timing diagrams, may comprise multiple bits in other examples. In this first timing diagram of <FIG>, the further transition bit <NUM> during time <NUM> is defined as a logical <NUM> (dominant) of <NUM> i.e. the slower baud rate bit time. At time <NUM> (in this example in the middle of the further transition bit at time <NUM> in line <NUM>) the CAN controller <NUM> or controller module <NUM> may affect the switch back to slow mode <NUM>. Accordingly, the mode switch signal at <NUM> and shown in line <NUM> becomes logical <NUM>, resulting in the unencoded transmit data from <NUM> being directed to the transmit output <NUM> by the switch <NUM>. The unencoded transmit data with the control module <NUM> providing a transmit signal at the slower baud rate is constant low for longer than the first time threshold, 110ns, and therefore the mode controller <NUM> will detect that the conditions are valid for a mode change to the slow mode <NUM> by transition <NUM>. The mode decoder provides the mode switch signal to logical <NUM> for the first transmitter <NUM> as shown in line <NUM> at time <NUM> and the mode switch signal to logical <NUM> for the second, slow transmitter <NUM> as shown in line <NUM> at time <NUM>. This results in the second transmitter <NUM> being enabled while the first, fast, transmitter <NUM> is disabled. The use of the slow transmitter means that the voltage level scheme applied to the CAN bus <NUM> changes from back to the first voltage level scheme that operated between <NUM> and <NUM> Volts ("dominant" and "recessive" CAN protocol levels) rather than -<NUM> Volts and +<NUM> Volts at time <NUM>. The CAN transceiver <NUM> is now in the slow mode <NUM>.

During time <NUM> to <NUM> the transmit data for the decoder <NUM> becomes static (no edges anymore) which is an invalid Manchester code and cannot be decoded. The decoder <NUM> may therefore maintain the last valid logic level <NUM>.

Turning to the example timing diagram of <FIG>, the timing diagram is identical to that of <FIG> except that the further transition bit <NUM> shown in line <NUM> at time period <NUM> is logic <NUM>, i.e. recessive according to the CAN protocol.

As will be recalled from the mode diagram of <FIG>, the mode detector <NUM> is configured to return the CAN transceiver <NUM> to the slow mode <NUM> if either the logic-high-time or the logic low time is longer than the first time threshold. Thus, the presence of the low baud rate transition bit <NUM>, whether it is logic high or logic low, with the non-encoded transmit data being provided to the CAN transceiver <NUM> is detected by the mode detector <NUM>.

Turning to the example timing diagram of <FIG>, an example transition between the CAN transceiver <NUM> slow mode <NUM> and the fast-RX mode <NUM> is shown. The timing diagram is substantially the same as that shown in <FIG> in terms of the signal values that are presented except the line <NUM> is not provided because the first transmitter is disabled during the fast-RX mode <NUM>. The same reference numerals to designate what the lines <NUM> - <NUM>, <NUM>, <NUM> show are used. The same reference numerals are used to show the periods of time to designate the arbitration phase <NUM>, the transition bit <NUM>, the further transition bit <NUM> and the slow mode <NUM>. The period between the transition bits <NUM> and <NUM> is shown as the receive data phase <NUM>.

The CAN controller module <NUM> and the CAN transceiver <NUM> start in slow mode. The transmit data of the controller module <NUM> is directed to the transmit output <NUM> via the switch <NUM> bypassing the encoder <NUM> when the mode signal at <NUM> is logical <NUM> as shown by the line <NUM> and the similarity between lines <NUM> and <NUM> during this time, until time <NUM>. The mode detector <NUM> in the transceiver <NUM> is in the slow mode and therefore the second, slow transmitter <NUM> is enabled as shown in line <NUM>, which represents the signal at <NUM>. The first, fast transmitter <NUM> is disabled in the slow mode <NUM> and therefore the line <NUM>, representing the mode-switch signal output at <NUM> is logical <NUM>. The output of the second, slow receiver <NUM> is directed to the receive output <NUM> via the switch <NUM> because the component of the mode switch signal at <NUM> is logical <NUM>. During the arbitration phase <NUM> and the beginning of the transition bit <NUM> the node may be operating as a traditional CAN node.

As mentioned above, after the arbitration phase <NUM> and before the receive data phase <NUM> a dedicated transition bit <NUM> may be defined in the CAN protocol frame and it is during this time the mode change is executed to switch the receiver arrangement to receive the higher baud rate signalling on the CAN bus <NUM>. At time <NUM> the CAN controller module <NUM> sets the controller mode signal at <NUM> to logical <NUM> as shown in line <NUM> and the switch <NUM> therefore directs the output of the encoder <NUM> to the transmit output <NUM> and therefore the transmit input <NUM>. Since the transition bit is a logical <NUM> (recessive) in line <NUM> at this time, the Manchester encoded transmit data from the encoder <NUM> becomes a pulse train with a pulse width of 50ns (determined by the <NUM> phase encoder clock), as shown in line <NUM> beginning at time <NUM>. In this example, the controller module <NUM> is configured to begin the change to the fast mode at time <NUM> because it is in the middle of the transition bit <NUM>, meaning the transmit data at <NUM> as shown in line <NUM> was already logical <NUM> for 500ns (up until time <NUM>). The first low pulse <NUM> on the line <NUM> is 50ns and this means the conditions are valid for a mode change from slow mode <NUM> to fast-RX mode <NUM> (see transition <NUM> in <FIG>) in the CAN transceiver <NUM>. It will be appreciated that the transition may not be at the middle but other parts of the transition bit.

The mode decoder <NUM> provides the mode control signals as shown in lines <NUM> and <NUM> to disable the first, fast transmitter <NUM> (which was already disabled) and disable the second, slow transmitter <NUM>. The mode switch signals also connect the first, fast receiver <NUM> to the receive output <NUM> via the switch <NUM>. The CAN transceiver <NUM> is now in fast-RX mode <NUM> with the transmitter arrangement <NUM> disabled and the receiver arrangement <NUM> in fast receive mode.

Between time <NUM> and <NUM> the second, slow transmitter <NUM> is still enabled and tries to follow the short pulses of 50ns in the encoded transmit data. Typically, the slow transmitter <NUM> was not designed to operate that fast and the output on the CAN bus cannot be predicted also resulting in unknow data <NUM> being received by the controller <NUM>. However, this may not a problem since all the controller <NUM> or controller module <NUM> in the CAN network are typically synchronised and can be configured to ignore received data during the transition bit <NUM>.

During the receive data phase <NUM>, the higher baud rate signalling from the CAN bus <NUM> is received by the fast receive <NUM> and passed to the CAN controller <NUM>.

At the end of the receive data-phase <NUM> there is also a dedicated transition bit <NUM>. In this timing diagram of <FIG>, the further transition bit <NUM> of line <NUM> during time <NUM> is defined as a logical <NUM> (recessive) of <NUM> i.e. the slower baud rate bit time. At time <NUM> (in this example in the middle of the further transition bit at time <NUM> in line <NUM>) the CAN controller <NUM> or controller module <NUM> may affect the switch back to slow mode. Accordingly, the mode switch signal at <NUM> and shown in line <NUM> becomes logical <NUM>, resulting in the unencoded transmit data from <NUM> being directed to the transmit output <NUM> by the switch <NUM>. The unencoded transmit data with the control module <NUM> providing a transmit signal at the slower baud rate is constant high for longer than the first time threshold, 110ns, and therefore the mode controller <NUM> will detect that the conditions are valid for a mode change to the slow mode <NUM> (see transition <NUM> in <FIG>). The mode decoder <NUM> provides the mode switch signal to logical <NUM> for the first transmitter (maintained disabled) as shown in line <NUM> at time <NUM> and the mode switch signal to logical <NUM> for the second, slow transmitter (now enabled) as shown in line <NUM> at time <NUM>. This results in the second transmitter <NUM> being enabled while the first, fast, transmitter <NUM> is (maintained) disabled. The slow receive mode is enabled.

Turning to the example timing diagram of <FIG>, the timing diagram is identical to that of <FIG> except that the further transition bit <NUM> shown in line <NUM> at time period <NUM> is logic <NUM>, i.e. dominant according to the CAN protocol.

Accordingly, optionally using a logic low or logic high signal to transition back to the slow mode, there may be be an optional active dominant signal on the bus <NUM> for a certain time, which might be useful system wide for the (re-)synchronization of the nodes. Thus, both logic high and logic low on line <NUM> are possible and optionally the CAN bus may be driven and/or the signal is filtered out by the transceiver.

<FIG> shows an example apparatus that includes a Controller Area Network, CAN, comprising a plurality of nodes including node <NUM> and other nodes <NUM>, <NUM>, <NUM>. The network apparatus may be an automobile or other apparatus and the CAN network may provide for communication between systems of the automobile or other apparatus.

<FIG> shows an example method of operating a Controller Area Network, CAN, transceiver configured to be connected to a CAN bus, the transceiver comprising a transmitter arrangement configured to transmit signalling on the CAN bus based on transmit data received by the transceiver, the transmitter arrangement comprising at least one transmitter configured to operate in a slow transmission mode or a fast transmission mode, wherein in the fast transmission mode the transmitter arrangement is configured to transmit said signalling at a higher baud rate than when the transmitter arrangement is in the slow transmission mode; and a receiver arrangement configured to receive signalling from the CAN bus and a receive output configured to provide received data to the CAN controller based on the received signalling and a decoder; the method comprising:.

<FIG> shows an example method of operating a Controller Area Network, CAN, controller configured to be connected to a CAN bus connected CAN transceiver, the CAN controller comprising 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 mode selector configured to provide a controller mode signal that instructs the CAN transceiver to operate in a fast transmission mode rather than a slow transmission mode, wherein the method comprises.

Claim 1:
A Controller Area Network, CAN, transceiver (<NUM>) configured to be connected to a CAN bus (<NUM>) comprising:
a transmit input (<NUM>) configured to receive transmit data from a CAN controller (<NUM>) for transmission on the CAN bus;
a transmitter arrangement (<NUM>) configured to transmit signalling on the CAN bus based on said transmit data, the transmitter arrangement comprising at least one transmitter (<NUM>) configured to operate in a first transmission mode or a second transmission mode, wherein in the first transmission mode the transmitter arrangement is configured to transmit said signalling with a first property and when the transmitter arrangement is in the second transmission mode the transmitter arrangement is configured to transmit said signalling with a second property, different to the first property;
a receiver arrangement (<NUM>) configured to receive signalling from the CAN bus;
a receive output (<NUM>) configured to provide received data to the CAN controller based on the received signalling; and
a mode detector (<NUM>);
wherein the mode detector (<NUM>) is coupled to the transmit input to receive the transmit data from the transmit input;
wherein the mode detector configured to determine the presence or absence of a first line code encoding of the transmit data;
wherein the transmitter arrangement is configured to operate in one of the first or second transmission modes (<NUM>, <NUM>) based on a determination of the mode detector that the transmit data is encoded with a first line code and configured to operate in the other of the first or second transmission modes based on a determination of the mode detector that the transmit data is not encoded with the first line code; and
wherein the mode detector is configured to provide a mode-switch signal to the transmitter arrangement to select either the first transmission mode or the second transmission mode;
wherein the transceiver includes a decoder (<NUM>) configured to decode the first line code of the transmit data and provide the decoded transmit data to the transmitter arrangement to provide for said transmission of the signalling on the CAN bus at least when the transmitter arrangement is in said one of the first or second transmission modes; and
wherein the first line code comprises a code which gives the transmit data shorter pulse widths than said transmit data that is not encoded with the first line code.