Vehicle-mounted system
Provided is a vehicle-mounted system capable of transmitting a command to a first system from a second system during a period in which the first system communicates with the second system according to a unidirectional communication protocol. A vehicle-mounted system 100 includes a sensor 10 (first system) and an ECU (second system). The sensor 10 outputs a message signal including a pause pulse to the communication line DATA according to SENT (a unidirectional communication protocol). The ECU 20 is connected to the communication line DATA, and transmits a command to the sensor 10 using the falling period of the pause pulse.
1. A vehicle-mounted system comprising a first system and a second system, wherein
the first system outputs a message signal including a pause pulse to a communication line according to a unidirectional communication protocol, and
the second system is connected to the communication line, and transmits a command to the first system using a falling period of the pause pulse.
2. The vehicle-mounted system according to claim 1 , wherein
the second system superimposes the command on the pause pulse by making the falling period of the pause pulse longer than a threshold.
3. The vehicle-mounted system according to claim 2 , wherein
the second system sets a content of the command by a length of the falling period of the pause pulse.
4. The vehicle-mounted system according to claim 2 , wherein
the second system superimposes the command on the pause pulse by increasing a number of falls of the pause pulse.
5. The vehicle-mounted system according to claim 4 , wherein
the second system sets a content of the command using a number of falls of the pause pulse.
6. The vehicle-mounted system according to claim 2 , wherein
the first system determines that the command has been transmitted from the second system when the falling period of the pause pulse is longer than the threshold.
7. The vehicle-mounted system according to claim 6 , wherein
the first system executes a predetermined process according to a length of the falling period of the pause pulse.
8. The vehicle-mounted system according to claim 6 , wherein
the first system executes a predetermined process according to a number of falls of the pause pulse.
9. The vehicle-mounted system according to claim 6 , wherein
the first system is an air flow sensor including a heater, and stops the heater when determining that the command has been transmitted from the second system.
10. The vehicle-mounted system according to claim 9 , wherein
the message includes a plurality of pieces of data to which an air flow signal indicating an air flow rate is allocated, and
the first system fixes at least one of the pieces of data at a predetermined value after stopping the heater.
11. The vehicle-mounted system according to claim 9 , wherein
the second system superimposes the command on the pause pulse after a CRC pulse when determining that a power source of a vehicle is in an idle state.
12. The vehicle-mounted system according to claim 9 , wherein
the first system includes an A/D converter, and changes an input range of the A/D converter according to the command when determining that the command has been transmitted from the second system.
13. The vehicle-mounted system according to claim 9 , wherein
the first system includes a pressure sensor and a humidity sensor, and stops a clock signal supplied to the pressure sensor and the humidity sensor or sets the pressure sensor and the humidity sensor in a standby state when determining that the command has been transmitted from the second system.
14. The vehicle-mounted system according to claim 1 , wherein
the pause pulse is a pulse configured to keep a length of the message constant.
15. The vehicle-mounted system according to claim 1 , wherein
the communication protocol is SENT.