The SENT (Single Edge Nibble Transmission) protocol is a relatively new protocol used in the automotive industry for transmitting sensor data to a controller. The SENT protocol is a one-way asynchronous voltage interface which requires three wires, a signal line, a supply voltage line and a ground line. SENT uses pulse width modulation to encode 4 bits (1 nibble) of data per symbol.
The basic unit of time in SENT is a tick, which can be between 3-90us. Each SENT message contains a sync period, made up of 5 low ticks and 56 high ticks, followed by up to 8 nibbles of data. Each data nibble is transmitted with a fixed-width low period of 5 ticks, followed by a variable-length high period from 12 to 27 ticks representing a nibbles value from 0 to 15. The data portion of the SENT message is make up of a status nibble, 1 to 6 nibbles of sensor measurements and a CRC nibble. Additionally, an option pause pulse can be used to compensate for variable message lengths.
Some of Microchip's newer PIC® microcontrollers, the dsPIC33EV256GM106 family for example, comes with a build-in SENT peripheral for transmitting or receiving SENT messages. The CCS C Compiler has build-in functions for setting up and using the SENT peripheral For these devices. The devices that have a SENT peripheral, the following functions will be available in the compiler for setting up and using the SENT peripheral: setup_sent(), sent_putd(), sent_getd() and sent_status().
The setup_sent() function is used to setup the SENT peripheral and has a parameter for setting up as an asynchronous SENT transmitter, synchronous SENT transmitter or a SENT receiver and the number of data nibbles to sent or receive. Other settings include whether to use the pause pulse.
The sent_putd() function is used to load the data nibbles to transmit when the peripheral is setup as a SENT transmitter, and the sent_getd() function is used to retrieve the data nibbles when the peripheral is setup as a SENT receiver. Finally, the sent_status() function is used to get the status of the SENT peripheral, for example what nibble it is currently transmitting or receiving.
The CCS C Compiler also provides two examples ex_sent_transmitter.c and ex_sent_receiver.c showing how use the SENT peripheral and built-in functions. ex_sent_transmitter.c is an example demonstrating how to setup and use the SENT peripheral as an asynchronous SENT transmitter, and ex_sent_receiver.c is an example show how to setup and use the SENT peripheral as a SENT receiver.
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