While current implementations usually follow a “round robin” interrogation, with sensors 0 through 3 polled in order (0,1,2,3…), it is entirely possible for any sequence to be established (e.g., 0,1,0,2,0,3…). The microcontroller can interrogate different sensors by varying the length of the MTP.
Only the sensor interrogated is expected to reply. The controller interrogates a sensor by emitting a logic-low MTP of the requisite length, then relinquishes the line for the sensor to reply. Each sensor is assigned a unique MTP length, which acts like an address. The MTP is the key to managing SENT SPC traffic. The SENT physical layer consists of a signal line, a +5 V supply voltage line, and a ground.
Note:Step-by-step procedures for using the Teledyne LeCroy serial trigger and decode options shown here can be found in the SENTbus Trigger, Decode, Measure/Graph and Eye Diagram Instruction Manual on our website.
This application note describes the SENT SPC protocol and demonstrates how to use an oscilloscope to verify a consistent Master Trigger Pulse (MTP) length. SENT SPC achieves this by introducing a new element into the SENT frame definition: the Master Trigger Pulse (MTP). To address the exponential increase in the number of sensors within a single vehicle, Infineon specified SENT Short PWM Code (SPC), a half-duplex variation of SENT that allows a single "master" microcontroller to manage up-to-four "slave" sensors on the same wire. Later specifications of SENT introduced Fast and Slow Channels to designate different streams of information carried within the same messages. Information lies within the width of the pulses. Instead, sensor signals are transmitted as a series of pulses, with data measured by falling-edge to falling-edge times. SENT was developed because the environment in a car was too noisy to transmit high resolution (10- or 12-bit) sensor data vertically on a 5 V bus. Single Edge Nibble Transmission protocol, more commonly known as SENT (SAE J2716 JAN201604), has long been used by the Automotive industry to report low-speed sensor data to the Engine Control Unit (ECU).