Overview of SENT (Single Edge Nibble Transmission) / SAE J2716
SENT is one of the automotive serial interfaces by SAE (Society of Automotive Engineers). It is a one-way, asynchronous, point to point digital interface, and starts to operate promptly after power-up. It is mainly replacing analog output sensors with 3P connectors with the lowest cost, and allows for high-resolution data with many features of sensor diagnostic information at both fast channel and slow channel and can meet functional safety ASIL up to C level. Official SAE page for SENT is linked here; https://www.sae.org/standards/content/j2716_201604/
There have been 4 times of revision in SENT specifications. The latest one, as of today, is APR 2016.
- SENT J2716 – APR 2016
- SENT J2716 – JAN 2010
- SENT J2716 – Feb 2008
- SENT J2716 – Apr 2007
Needs to pay to see the full version of the specification, as noted in the SAE page.
Revision Comparison between JAN 2010 and APR 2016
Revision JAN 2010 is being widely used in sensors/modules, especially in automotive applications. It is in the transition of a newer version, APR 2016. The purpose of this posting is to find differences between these two revisions. A frequent question, engineers can encounter, might be whether he can use JAN 2010 SENT block of ASSP/ASIC in use to meet the requirements of the newer version, APR2016. The answer can be positive in most cases, as these two are not so much different. However, must know exactly what they are, and where it can have gaps.
The rationale on the cover page of APR2016 specification describes the new features /additions. It can be technical revisions or just editorial changes. More focus on technical revisions in this posting.
- Clarified clock variation refers to variation in clock tick time.
- New appendix for high-speed 12bit sensors.
- Changes for initialization and non-usage of serial message.
- Changes to support option for independent 5V supply in sensor.
- Serial message cycle changed to <= 64 messages for greater flexibility and to allow more time for diagnostic information.
- Clarification to EMC susceptibility testing guidelines for erroneous SENT frames which remain undetected by the SENT CRC.
- Added Appendix A.6 temperature sensor requirements.
- Added Appendix E.
- Added Appendix G for recommended connector.
- Created Appendix H (SENT Data Frame Formats) and moved generic sensor requirements from Appendix A to Appendix H.
- Changes to support higher current sensors.
- Added E.3 error messages and signals.
- Added A.7 position sensors and combined position temperature sensors.
- Added overview of SENT standard structure.
The table below summarizes most of the technical revision changes with some comments on how to use the old JAN 2010 version to meet the new APR 2016 requirements.
| No | Rationale in APR 2016 | Comparision | Comments / Remarks | ||
| JAN 2010 | APR 2016 | Ref | |||
| 1 | Clarified clock variation refers to variation in clock tick time | Clock Jitter and Drift Error; <= 0.05us variation of max nibble time (27 clock tick) compared to the expected time derived from the calibration pulse time at a 3us clock tick. <= 0.25us variation of max nibble time (27 clock tick) compared to the expected time derived from the calibration pulse time at a 10us clock tick. |
Clock Jitter and Drift Error; <= 0.3us variation of max nibble time (27 clock tick) compared to the expected time derived from the calibration pulse time at a 3usec clock tick. |
6.2 Clock Tolerance | APR 2016 requirement looks to be weaker than JAN 2010. |
| 2 | New appendix for high speed 12bit sensors | N/A | New application protocol for single high speed 12bit data with shorter SENT data frames. The highest speed with worst-case message length is less than 500us without serial message. It can be less than 550us with serial message channel enabled. | Appendix H / H.3 | Not a normal configuration in SENT protocol. If needs to send data, 2x faster than 1ms, this example can be considered for single-channel data transmission. |
| 3 | Changes for initialization and non-usage of serial message | Enhanced Serial Message Format; The frame start of a serial message is indicated by the unique pattern “01111110” in bit 3 of the status and communication nibble. The first “1” in a series of six ones indicates the first nibble of a serial message frame. |
Enhance Serial Message Format; The frame start of a serial message is indicated by the unique pattern “01111110” in bit 3 of the status and communication nibble. The first “1” in a series of six ones indicates the first nibble of a serial message frame. The “0” in SENT message #13 is defined to ensure the uniqueness of the start pattern. At initialization, it is recommended that the transmitter send the Serial data bit #3 sequence “0…01111110” (start with one or more SENT messages equivalent to #18). One starting “0” will guarantee the minimum latency start sequence and no interrupted message (due to sensor reset) will appear to be completed and incorrectly pass the CRC. |
5.2.4.2 | Additional requirements (serial data message, starting with “01111110”) added in APR 2016. But this one can be generally considered and implemented in the SENT block (starts always with “01111110” in a serial message after power-up). Needs to check it when using JAN 2010 specification. |
| N/A | Non-usage of Serial Message; If no serial message is to be transmitted, both serial data bits shall be set to zero for both formats. If the transmitter needs to interrupt an already commenced data sequence, it is the responsibility of the transmitter to ensure that the serial message to be received fails the checksum calculation by corrupting either the data or CRC transmitted. This requirement is not intended to cover transmitter resets. |
5.2.4.4 | 5.2.4.4 is a new addition in APR2016. Maybe no issue with JAN 2010 for most of the applications as serial messages are enabled for all operating time after power-up. | ||
| 4 | Changes to support option for independent 5V supply in sensor | Average current consumption from Receiver supply over one message; I_sup <= 20mA T_fall <= 6.5us |
Average current consumption from Receiver 5V supply over one message; I_sup <= 50mA T_fall <= 6.5us @I_sup <= 20mA T_fall <= 5.0us @I_sup <= 50mA |
6.3.1 / Table 6.3.1-1 |
Most of the sensors having SENT interface is consuming current, less than 20mA. |
| 5 | Serial message cycle changed to <= 64 messages for greater flexibility and to allow more time for diagnostic information | One serial message cycle shall be composed of <= 32 messages. | One serial message cycle shall be composed of <= 64 messages. | Appendix D / D.6 |
Needs to limit maximum serial messages below 32 to be compatible for both JAN 2010 and APR 2016. |
| 6 | Clarification to EMC susceptibility testing guidelines for erroneous SENT frames which remain undetected by the SENT CRC | Describes Appendix C (EMC susceptibility) over two paragraphs, C.1 / C.2 | Describes Appendix C (EMC susceptibility) over C.1 / C.1.1 / C.1.2 / C.1.2.1 / C.1.2.2 / C1.3 / C1.3.1 / C.1.3.2 / C.2 with more details & descriptions | Appendix C | No technical change. Added more descriptions, test setups, pass-fail criteria. Needs to work on each application with the system makers. |
| 7 | Added Appendix A.6 Temperature Sensor requirements | N/A | Added; A.6 Temperature Sensors |
Appendix A / A.6 |
|
| 8 | Added Appendix E | N/A. Definitions that apply to multiple application-specific protocols from Appendix A (JAN 2010) are in Appendix E in APR2016. |
Appendix E common sensor definitions; The contents partially described in JAN2010 version are generalized to apply to each application. Function, data, error, etc. are defined in detail. |
Appendix E | |
| 9 | Added Appendix G for recommended connector | N/A | Provides the mechanical and electrical specifications for the SENT transmitter connectors and pin configurations that can be optionally applied. | Appendix G | Just use it as a reference. |
| 10 | Created Appendix H (SENT Data Frame Formats) and removed generic sensor requirements from Appendix A to Appendix H | Appendix A is having a description on SENT data frame format. | Part of Appendix A in JAN2010 moved to Appendix H and describes SENT data frame formats; H.1 Two 12-bit fast channels. H.2 One 12-bit fast channel H.3 High-speed with one 12-bit fast channel. H.4 Secure sensor with 12-bit fast channel 1 and secure sensor information on fast channel 2. H.5 Single sensor with 12-bit fast channel 1 and zero value on fast channel 2. H.6 Two fast channels with 14-bit fast channel 1 and 10-bit fast channel 2. H.7 Two fast channels with 16-bit fast channel 1 and 8-bit fast channel 2. |
Appendix H | |
| 11 | Changes to support higher current sensors | Only one option, regulated 5V supply from SENT receiver. | More options are added, mainly to supply more current to SENT transmitter. Regulated 5V supply from SENT receiver, Independent 5V power supply in a receiver with several different grounding concepts. | 6.3.1 | |
| 12 | Added E.3 error messages and signals | Appendix A contains error messages example | Appendix H has error messages and signals. | Appendix E / E.3 |
Needs to work with system makers. These requirements mainly coming from system-level ECU. |
| 13 | Added A.7 position sensors and combined position temperature sensors | N/A | A.7 Position Sensors and Ratio Sensors | Appendix A / A.7 |
|
| 14 | Added overview of SENT standard structure | N/A | 3.2 Overview of SENT Standard Structure | 3.2 | Editorial change. |