Freescale Semiconductor

Application Note

Document Number: AN4856

Rev. 0, 03/2014

Contents

1 Introduction

This application note describes the SENT/SPC driver for

the MPC574xP 32-bit microcontrollers. It also provides

information on the Single Edge Nibble Transmission

protocol (SENT, SAE J2716), along with its Short PWM

Code (SPC) enhancement. Additionally, the driver

implementation, API, and functional description are also

discussed in this application note.

The information about the SENT protocol has been

derived from the SAE J2716 Surface Vehicle

Information Report, JAN2010.

The information about the SPC enhancement has been

derived from the TLE4998C Data Sheet, Rev 1.0,

December 2008.

The MPC574xP SENT/SPC driver itself and the

example application are part of the AN4856SW package.

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.1 SENT encoding scheme . . . . . . . . . . . . . . . . . . . . . 2

2.2 SPC protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3 SENT physical layer . . . . . . . . . . . . . . . . . . . . . . . . 7

3 MPC574xP SENT/SPC Driver. . . . . . . . . . . . . . . . . . . . . 9

3.1 Utilized MPC574xP peripherals. . . . . . . . . . . . . . . . 9

3.2 SPC bidirectional communication . . . . . . . . . . . . . . 9

3.3 Driver configuration . . . . . . . . . . . . . . . . . . . . . . . . 11

3.4 Application programming interface . . . . . . . . . . . . 12

3.5 Functional description . . . . . . . . . . . . . . . . . . . . . . 21

3.6 Memory allocation . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.7 Application example . . . . . . . . . . . . . . . . . . . . . . . 33

4 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

6 Acronyms and Definitions . . . . . . . . . . . . . . . . . . . . . . . 36

MPC574xP SENT/SPC Driver

by: Josef Kramoliš

MPC574xP SENT/SPC Driver, Rev. 0

Overview

Freescale Semiconductor2

2 Overview

The Single Edge Nibble Transmission protocol is targeted for use in those applications where

high-resolution data is transmitted from a sensor to the ECU. It can be considered as an alternative to

conventional sensors providing analog output voltage, and for PWM output sensors. It can also be

considered as a low-cost alternative to the LIN or CAN communication standards.

Applications for electric power steering, throttle position sensing, pedal position sensing, airflow mass

sensing, liquid level sensing, etc., can be used as examples of target applications for SENT-compatible

sensor devices.

2.1 SENT encoding scheme

SENT is a unidirectional communication standard where data from a sensor is transmitted independently

without any intervention of the data receiving device (for example, the MCU). A signal transmitted by the

sensor consists of a series of pulses, where the distance between consecutive falling edges defines the

transmitted 4-bit data nibble representing values from 0 to 15. Total transmission time is dependent on the

transmitted data values and on the 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 CRC nibble is also the leading falling edge of the consecutive SENT transmission

synchronization/calibration pulse – see Figure 1).

A SENT communication fundamental unit of time (unit time – UT, nominal transmitter clock period) can

be in the range of 3–90 s, according to the SAE J2716 specification. The maximum allowed clock

variation is ± 20% from the nominal unit time, which allows the use of low-cost RC oscillators in the

sensor device.

NOTE

A 3 s fundamental unit time will be considered as nominal for unification

of further timing descriptions.

The transmission sequence consists of the following pulses:

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)