20 Single-Edge Nibble Transmission (SENT)

Note: This data sheet summarizes the features of this group of dsPIC33CK512MPT608 family devices. It is not intended to be a comprehensive reference source. To complement the information in this data sheet, refer to “Single-Edge Nibble Transmission (SENT) Module” (www.microchip.com/DS70005145) in the “dsPIC33/PIC24 Family Reference Manual”.

The Single-Edge Nibble Transmission (SENT) module is based on the SAE J2716, “SENT – Single-Edge Nibble Transmission for Automotive Applications”. The SENT protocol is a one-way, single wire, time-modulated serial communication based on successive falling edges. It is intended for use in applications where high-resolution sensor data need to be communicated from a sensor to an Engine Control Unit (ECU).

The SENTx module has the following major features:

  • Selectable Transmit or Receive mode
  • Synchronous or Asynchronous Transmit modes
  • Automatic Data Rate Synchronization
  • Optional Automatic Detection of CRC Errors in Receive mode
  • Optional Hardware Calculation of CRC in 
Transmit mode
  • Support for Optional Pause Pulse Period
  • Data Buffering for One Message Frame
  • Selectable Data Length for Transmit/Receive, 
Up to Six Nibbles
  • Automatic Detection of Framing Errors

SENT protocol timing is based on a predetermined time unit, TTICK. Both the transmitter and receiver must be preconfigured for TTICK, which can vary from 3 to 90 µs. A SENT message frame starts with a Sync pulse. The purpose of the Sync pulse is to allow the receiver to calculate the data rate of the message encoded by the transmitter. The SENT specification allows messages to be validated with up to a 20% variation in TTICK. This allows for the transmitter and receiver to run from different clocks that may be inaccurate, and drift with time and temperature. The data nibbles are four bits in length and are encoded as the data value + 12 ticks. This yields a 0 value of 12 ticks and the maximum value, 0xF, of 27 ticks.

A SENT message consists of the following:

  • A synchronization/calibration period of 56 tick times
  • A status nibble of 12-27 tick times
  • Up to six data nibbles of 12-27 tick times
  • A CRC nibble of 12-27 tick times
  • An optional pause pulse period of 12-768 tick times

Figure 20-1 shows a block diagram of the SENTx module.

Figure 20-2 shows the construction of a typical 6-nibble data frame, with the numbers representing the minimum or maximum number of tick times for each section.

Figure 20-1. SENTx Module Block Diagram
Figure 20-2. SENTx Protocol Data Frames