Do you know the difference between high-speed CAN and low-speed, fault-tolerant CAN?
Recently, Engineer Li from a company in Guangzhou contacted us and said that he found our USBCAN analyzer could not communicate with his CAN bus. After the after-sales technical support engineer and Li Gong confirmed it, the reason was found. His device uses low-speed, fault-tolerant CAN communication, which couldn’t communicate with our standard high-speed CAN bus analyzer.
Figure 2 High-speed CAN signal
Figure 3 Low-speed CAN signal
How do you tell the device to use high-speed CAN or low-speed, fault-tolerant CAN?
1. Fault-tolerant CAN and high-speed CAN are different in the range of supported baud rates. High-speed CAN supports a baud rate of 5k-1M, but fault-tolerant CAN only supports a baud rate of 5K-125K.
If your device cannot communicate with high-speed CAN devices and the baud rate is between 5K and 125K, it is very likely that your device is using low-speed, fault-tolerant CAN communication.
2. The voltages of CAN_H and CAN_L with respect to ground are also different in high-speed CAN and low-speed, fault-tolerant CAN.
When the bus is in idle state, the voltages of CAN-H and CAN-L with respect to ground in high-speed CAN are both about 2.5V, while the voltage of CAN-L with respect to ground in low-speed, fault-tolerant CAN is about 5V, and the voltage of the CAN-H with respect to ground is about 0V.
When the bus is in valid state, the voltage of CAN-H with respect to ground is about 3.6V, the voltage of CAN-L with respect to ground is about 1.4V in high-speed CAN, and the voltage of CAN-H with respect to ground in is about 4V, and the voltage of CAN-L to ground is about 1V in low-speed, fault-tolerant CAN.
If your device cannot communicate with high-speed CAN devices and the baud rate is between 5K and 125K, it is very likely that your device is using low-speed, fault-tolerant CAN communication.
2. The voltages of CAN_H and CAN_L with respect to ground are also different in high-speed CAN and low-speed, fault-tolerant CAN.
When the bus is in idle state, the voltages of CAN-H and CAN-L with respect to ground in high-speed CAN are both about 2.5V, while the voltage of CAN-L with respect to ground in low-speed, fault-tolerant CAN is about 5V, and the voltage of the CAN-H with respect to ground is about 0V.
When the bus is in valid state, the voltage of CAN-H with respect to ground is about 3.6V, the voltage of CAN-L with respect to ground is about 1.4V in high-speed CAN, and the voltage of CAN-H with respect to ground in is about 4V, and the voltage of CAN-L to ground is about 1V in low-speed, fault-tolerant CAN.
Figure 4 GCAN-403 low-speed, fault-tolerant converter
Don’t be worry if you find your device is using low-speed, fault-tolerant, a GCAN-403 converter can helps.
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