SENT - Single Edge Nibble Transmission for Automotive Applications
J2716
This document defines a level of standardization in the implementation of the digital pulse scheme for reporting sensor information via Single Edge Nibble Transmission (SENT) encoding. This standard will allow ECU and tool manufacturers to satisfy the needs of multiple end users with minimum modifications to the basic design. This standard will benefit vehicle Original Equipment Manufacturers (OEMs) by achieving lower ECU costs due to higher industry volumes of the basic design. Requirements stated in this document provide a minimum standard level of performance to which all compatible ECUs and media shall be designed. This assures data communication among all connected devices regardless of supplier. This document is a communication interface specification and no to be treated as product specification. The intended audience includes, but is not limited to, ECU suppliers, sensor suppliers, component release engineers and vehicle system engineers.
Rationale: 1. Clarified items.
2. New requirement for SENT to implement a third CRC calculation method.
3. A new protocol called SENT-B is defined as an alternative option to the current SENT protocol. The following objectives are the base of the new SENT-B protocol design:
• Like the current SENT protocol, the SENT-B protocol is a low-cost unidirectional communications scheme from sensor / transmitting device to controller /receiving device. Differing from SENT protocol, SENT-B also uses the time between rising edges to code the data transmission. This allows higher data coding density and so higher data rates and thus the use for applications where SENT protocol is not fast enough.
• The physical layer hardware of the receiver is compatible between SENT and SENT-B protocols. This applies to the controlled threshold digital receiver and to the receiver interface circuit topology (pull-up behavior and input impedance). That way, transmitters implementing SENT and SENT-B protocols can both be connected to the same receiver input.
• However, the decoder logic in the microprocessor (whether software of dedicated hardware) will be significantly different to decode SENT-B.
• SENT-B allows the efficient transmission of frames with configurable size, holding up to 56 bits of data, plus a 7-bit CRC.
• With a 3 microseconds Tick Time, a SENT frame with two 12-bit fast channels and a 4-bit status and communication nibble and pause pulse (constant frame length – 282 ticks) results in a net data rate of 28.4 kbit/s and a frame rate of 1182 frame/s. A similar SENT-B frame results in a net data rate of 56.3 kbit/s and a frame rate of 2347 frame/s.
• At identical data transmission rates, the SENT-B protocol can potentially achieve better EMC performance (i.e., radiated emissions and immunity) compared to the SENT protocol, as the clock tick time duration can be increased by a factor of approximately 2.
