Component Functional Description - Sent Sensor

GENERAL INFORMATION:  SENT (Single edge nibble transmission) communication is a unidirectional protocol supporting communications from smart sensors to the PCM (Powertrain Control Module). SENT is a simpler and lower-cost alternative to other sensors using the CAN and LIN networks because SENT sensors are one directional and the SENT protocol overcomes some of the deficiencies of PWM (Pulse Width Modulation). Automotive systems use serial data transmissions to enable the rapid transfer of information between engine sensors and PCM. The SENT bus is a serial data standard managed and developed by SAE International as a low-cost digital point-to-point interface for unidirectional sensor data. SENT sensors are gaining popularity for transiting high resolution data between automotive sensors and controllers. They can provide digital readings of temperature, pressure, throttle position, and air flow in a single sensor. During normal operation, the SENT sensor is powered up and the internal transceiver automatically starts transmitting the SENT data to the PCM. This is very similar to the model of an analog output, with one important difference, SENT data is not limited to one data parameter per transmission and can easily report multiple pieces of additional information, such as temperature, pressure, position, air flow, production codes, diagnostics, and other secondary data.

GENERAL OPERATION:  The SENT sensor requires three wires to operate:

1. Supply voltage (5V).
2. Ground.
3. Signal (low state < 0.5V, high state > 4.1V). The signal voltage is one direction, from the sensor to the receiving Electronic Control Unit (ECU).

Depending on the vehicle application, the SENT sensor can provide high-resolution data of the temperature, pressure, throttle position, and air flow. The PCM provides the SENT sensor with a 5-Volt reference and a sensor ground circuit. The sensor is hard-wired to the PCM. The sensor sends an output digital signal to the PCM.

SENT high-resolution data communication detail:  Data from the SENT sensor is transmitted independently without any intervention of the data receiving device (e.g. PCM). The signal transmitted by the sensor consists of a series of pulses, where the distance between consecutive falling edges defines the transmitted data nibble (unit of 4 bits) representing values from 0 to 15. Total transmission time is dependent on the transmitted data values and on clock variation of the transmitter (sensor). A consecutive SENT transmission starts immediately after the previous transmission ends the trailing falling edge of the SENT transmission.

The SENT protocol message consists of a sequence of pulses that are sent by the control module repeatedly after a specified pause pulse, in the same pattern, to identify the stop and start of each new SENT message. A single SENT message is a series of nibbles consisting of the following fields/pulses as described below:

1. Synchronization/Calibration pulse (56 unit times).
2. 4-bit Status nibble pulse (12 to 27 unit times).
3. Up to six 4-bit Data nibble pulses (12 to 27 unit times each).
4. 4-bit Checksum nibble pulse (12 to 27 unit times).