Microcontroller with can bus module and auto speed detect
In a method for initializing a Controller Area Network (CAN) module in a microcontroller, the following steps may be provided: measuring the period times between a plurality of falling or rising edges of a CAN signal; sorting the period times; determining difference values between adjacent period times of the sorted period times; sorting the difference values; selecting a first difference value from the sorted difference values and determining a first frequency from the first difference value; initializing the CAN module using the selected frequency; receiving a CAN signal frame; determining whether an error occurred; if an error occurred selecting a next frequency and repeating initializing the CAN module until a valid CAN frequency has been found.
1. A method for initializing a Controller Area Network (CAN) module in a microcontroller,
the method comprising:
measuring period times between a plurality of falling or rising edges of a CAN signal;
sorting said period times by their respective value;
determining difference values between adjacent period times of said sorted period times;
sorting said difference values by their respective value;
selecting a first difference value from said sorted difference values and determining a first frequency from said first difference value;
initializing said CAN module using said selected frequency;
receiving a CAN signal frame;
determining whether an error occurred;
in response to said determining of an error, selecting a next difference value from said sorted difference values and determining an associated frequency and repeating initializing the CAN module until a valid CAN frequency has been found.
2. The method according to claim 1 , further comprising coupling an external CAN line with an input of a capture module of said microcontroller to measure said period times.
3. The method according to claim 1 , further comprising feeding a CAN signal internally to an input of a capture module of said microcontroller to measure said period times.
4. The method according to claim 3 , wherein ten period times between falling edges of a CAN signal are measured.
5. The method according to claim 1 , further comprising after the step of sorting said difference values, the step of:
discarding difference values that result in invalid frequencies.
6. The method according to claim 1 , wherein a timer and capture unit is used to measure the period times.
7. The method according to claim 1 , wherein the method is repeated if no valid frequency is found.
8. The method according to claim 1 , wherein the step of determining a frequency from said difference value is performed using a look-up table.
9. The method according to claim 1 , wherein the step of determining a frequency from said difference value uses rounding or truncation to calculate a frequency.
10. The method according to claim 1 , further comprising the step of programming the microcontroller to perform the method.
11. The method according to claim 1 , wherein the microcontroller comprises a state machine and further comprising the step of performing the method by the state machine.
12. A microcontroller comprising:
a central processing unit (CPU)
a Controller Area Network (CAN) module,
a timer;
a capture module coupled with said timer;
wherein the microcontroller is configured to automatically detect a CAN frequency by:
measuring the period times between a plurality of falling or rising edges of a CAN signal;
sorting said period times by their respective value;
determining differences between adjacent period times of said sorted period times;
sorting said determined differences by their respective value;
selecting a first difference from said sorted difference values and determining a first frequency from said first difference;
initializing said CAN module using said selected frequency;
receiving a CAN signal frame;
determining whether an error occurred;
in response to said determining of an error, selecting a next difference and determining an associated frequency and repeating initializing the CAN module until a valid CAN frequency has been found.
13. The microcontroller according to claim 12 , wherein the microcontroller is further configured to discard difference values that result in invalid frequencies.
14. The microcontroller according to claim 12 , wherein the capture module comprises an edge detector controlling a driver which couples said timer with a capture register.
15. The microcontroller according to claim 12 , comprising a controllable driver coupled between an input of the CAN Bus module and the input of said capture module.
16. The microcontroller according to claim 12 , wherein the microcontroller is configured to determine a frequency from said difference value by using a look-up table.
17. The microcontroller according to claim 12 , wherein the microcontroller is configured to determine a frequency from said difference value using rounding or truncation.
18. The microcontroller according to claim 12 , wherein the microcontroller is programmed by software to determine said CAN frequency.
19. The microcontroller according to claim 12 , comprising a state machine to determine said CAN frequency.
20. The microcontroller according to claim 19 , comprising a special function register to control the state machine.
21. A method for initializing a Controller Area Network (CAN) module in a microcontroller,
the method comprising:
receiving a CAN signal comprising a plurality of consecutive periods;
measuring the plurality of consecutive period times of the CAN signal, wherein a period is defined as the time between two consecutive falling or two consecutive rising edges of the CAN signal;
sorting said period times by their respective value;
determining difference values between adjacent period times of said sorted period times;
sorting said difference values by their respective value;
selecting a first difference value from said sorted difference values and determining a first frequency from said first difference value;
initializing said CAN module using said selected frequency;
receiving a CAN signal frame;
determining whether an error occurred;
in response to said determining of an error, selecting a next difference value and determining an associated frequency and repeating initializing the CAN module until a valid CAN frequency has been found.