SENT (protocol)

The SAE J2716 SENT (Single Edge Nibble Transmission) protocol [1] is a point-to-point scheme for transmitting signal values from a sensor to a controller. It is intended to allow for transmission of high resolution data with a low system cost.

Hardware

The SENT protocol is a one-way, asynchronous voltage interface which requires three wires: a signal line (low state < 0.5V, high state > 4.1V), a supply voltage line (5V) and a ground line. SENT uses Pulse Width Modulation to encode 4 bits (1 nibble) per symbol.

The basic unit of time in SENT is called a tick, where a tick can be between 3 - 90 µs, at the sender's option. Each message is preceded by a calibration pulse with a high period of 56 ticks for framing and calibration of tick length. After the calibration pulse, each nibble is transmitted with an fixed-width low signal, followed by a variable-length high period. The low-period is 5 (or more) ticks in length, while the high period can vary between 12-27 ticks (representing nibbles ranging from 0-15.)[2]

Software

Data is transmitted in units of 4 bits (1 nibble) for which the interval between two falling edges (single edge) of the modulated signal with a constant amplitude voltage is evaluated. A SENT message is 32 bits long (8 nibbles) and consists of the following components: 24 bits of signal data (6 nibbles) that represents 2 measurement channels of 3 nibbles each (such as pressure and temperature), 4 bits (1 nibble) for CRC error detection, and 4 bits (1 nibble) of status/communication information. Optionally, data can be transferred in 20 bit messages (5 nibbles) composed of a single 12 bit (3 nibble) measurement, a 4 bit (1 nibble) CRC error checksum, and a 4 bit (1 nibble) status/communication field.

The image below shows the SENT signal described above. In this case a Pause Pulse is used. The Pause Pulse compensates for the varying length of the messages.

See also

References
  1. SENT: official SAE page
  2. White, Tim (2014). "A Tutorial for the Digital SENT Interface". IDT. Retrieved 12 Aug 2020.


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