STM32 CAN Baud Rate Calculator
Usually 1.5, 2, 2.5, etc. Must be >= 1.5
e.g., 8 to 256. This is the sum of Sync_Seg, Prop_Seg, Phase_Seg1, Phase_Seg2.
Understanding STM32 CAN Baud Rate Calculation
The Controller Area Network (CAN) bus is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other's applications without a host computer. Calculating the correct baud rate for your STM32 microcontroller's CAN peripheral is crucial for reliable communication. The baud rate determines how many bits can be transmitted per second over the CAN bus.
Key Concepts:
- System Clock Frequency (Hz): This is the primary clock frequency supplied to the CAN peripheral on your STM32 microcontroller.
- Time Quantum (Tq): The fundamental unit of time in CAN communication. All bit timings are measured in multiples of Time Quanta.
- Prescaler (Tq_PS): This value divides the system clock frequency to generate the Time Quantum. The formula is:
Tq = System Clock Frequency / Prescaler. Note that the Prescaler in STM32 CAN is often represented as a floating-point value (e.g., 1.5, 2.5) which is handled internally by the peripheral to derive the actual clock division. - Time Segments: The CAN protocol divides each bit into three distinct time segments:
- Synchronization Segment (Sync_Seg): Used for synchronizing nodes on the bus.
- Propagation Segment (Prop_Seg): Accounts for the physical delay of the bus.
- Phase Segment 1 (Phase_Seg1): Used for sample point adjustment.
- Phase Segment 2 (Phase_Seg2): Also used for sample point adjustment.
- Total Time Quanta (Tq_TS): The sum of all time segments:
Tq_TS = Sync_Seg + Prop_Seg + Phase_Seg1 + Phase_Seg2. This value must be between 8 and 256. - Sample Point: This is the point within a bit period where the receiver samples the bus level to determine if it's a dominant (0) or recessive (1) bit. It's typically located at the end of Prop_Seg or Phase_Seg1.
- Baud Rate: The number of bits transmitted per second. It's calculated as:
Baud Rate = 1 / (Bit Period), whereBit Period = Tq_TS * Tq.
How to Use the Calculator:
- Enter your STM32's System Clock Frequency in Hertz (e.g., 72,000,000 Hz for an STM32F103 at 72MHz).
- Specify the Prescaler value. This is a crucial parameter. For STM32 CAN, it's often set to a value like 1.5, 2, 2.5, etc., up to 1024 in integer terms for clock division. The calculator uses the direct division factor. Ensure this value is greater than or equal to 1.5.
- Input the total desired Time Segments (Tq_TS). This is the sum of Sync_Seg, Prop_Seg, Phase_Seg1, and Phase_Seg2. A common value is 16 (e.g., 1 + 1 + 13 + 1, or 1 + 1 + 8 + 6). The total must be between 8 and 256.
- Click "Calculate Baud Rate". The tool will output the calculated baud rate in bits per second (bps).
Example:
Let's say you have an STM32 running at a System Clock Frequency of 72,000,000 Hz. You want to achieve a common baud rate like 500 kbps (500,000 bps). You've determined through experimentation or datasheet lookup that a Prescaler of 1.5 and a total of Time Segments of 16 (e.g., Sync_Seg=1, Prop_Seg=1, Phase_Seg1=13, Phase_Seg2=1) is suitable.
Plugging these values into the calculator:
- System Clock Frequency: 72,000,000 Hz
- Prescaler: 1.5
- Time Segments: 16
The calculator would output a Baud Rate. If the output is 500,000 bps (or 500 kbps), these settings are correct for your desired baud rate.