Typical use cases 

The SENT standard is used in modern vehicles where high-resolution sensor data is required. This includes, for example, pressure or temperature sensors for interior climate control, temperature sensors in the engine compartment, or mass airflow sensors. SENT proves to be particularly reliable in environments with strong electromagnetic interference and is therefore frequently used in powertrain technology.

Figure 1: The SENT physical layer with power, signal and ground.

SENT in detail: Physical principles 

Technically, SENT is based on a three-wire interface consisting of a signal line, a supply voltage for the sensor, and ground. Signaling is not achieved via data packets in the traditional sense, but rather by measuring the time intervals between falling signal edges (PWM). The time base, known as the tick, ranges from 3 to 90 microseconds and is defined by the transmitting device. To ensure the receiver can accurately determine the actual tick length, each frame begins with a synchronization and calibration period of 56 ticks. A symbol, or nibble, always comprises a fixed low phase of approximately five ticks and a variable high phase. The nibble value is calculated by subtracting twelve from the total number of ticks, based on the total duration between two edges.

Figure 2: The typical SENT signal waveform.

A typical fast-channel frame consists of eight nibbles, or 32 bits. It contains a status nibble, two measurement channels with twelve bits each, and a CRC nibble for error detection. An optional pause can be inserted at the end of the frame to ensure that the overall duration per frame remains constant. In addition to the fast channel, which transmits measurement data, there is also a slow channel that provides supplementary information such as diagnostic values or calibration data via the status bits. This data is transmitted fragmentarily across multiple fast-channel frames, thus complementing the main transmission.

Figure 3: Example setup of a fast-channel frame.

Data rate and performance

The data rate of SENT is not fixed, but depends on the tick length and the selected pauses. With a tick of 3 microseconds and an average nibble of approximately 20 ticks, the resulting frame time is around 0.65 milliseconds. This corresponds to a frame frequency of approximately 1.5 kilohertz and a net data rate of around 37 kilobits per second for 24 bits of user data. Thus, SENT offers a significantly higher resolution than analog signals, but remains far below the transmission rates of CAN FD or Automotive Ethernet.

The advantages of SENT include its extremely low hardware complexity, requiring only a single signal line, the robustness of its time coding against interference, and the deterministic nature of its transmission. Furthermore, resolutions of typically twelve bits per measurement channel can be achieved without the expense of a full-fledged bus interface. The integration of diagnostic data via the slow channel also enhances its utility. However, these advantages are offset by several disadvantages: SENT is a purely output-based protocol without a feedback channel, meaning that parameterization or queries are only possible via additional interfaces. Moreover, communication is strictly designed as a point-to-point connection, and bus structures like those used in LIN or CAN are not supported. Finally, the achievable data rate remains limited compared to modern bus systems.
Powerful tools are now available for testing and commissioning SENT systems. Modern oscilloscopes and PC-based protocol decoders support the analysis of SENT signals by automatically calibrating ticks, decoding nibbles, and performing CRC checks. This significantly simplifies troubleshooting, EMC analysis, and quality assurance in end-of-line testing. SENT remains relevant for the future: The "SENT-B" revision currently under development will enable approximately double the speed, thus opening up additional application areas.

Figure 4: Many more gateway combinations can be implemented with the Mobilizer via the SENT interface.

Use SENT with the Automotive Gateway Ixxat Mobilizer

HMS Networks supports the use of SENT-based sensors through its new Ixxat Mobilizer Automotive Gateway product family. With its diverse range and number of IVN interfaces, as well as integrated simulation and automation capabilities, this product family offers an ideal solution platform for automotive testing tasks. This allows for the creation of applications that can combine vehicle data from CAN FD, LIN, K-Line, Automotive Ethernet, and FlexRay networks with sensor data. Furthermore, automation systems can be integrated via EtherCAT or Generic Ethernet. Vehicle data can also be logged and exported for analysis. Using the Advanced Configuration Tool (ACT), engineers can easily configure all solutions and create standalone applications without requiring programming knowledge.

More information about the Automotive Gateway Ixxat Mobilizer can be found here:

Ixxat Mobilizer