Long-distance can communication termination resistance strategy

Help coal mine customers adjusted for many years terminal resistance, summed up some of the experience for everyone to reference, no reference theory, but are the result of practice.

About the terminal resistor: We always remember can terminal to add 120 euro, but that is a short distance impedance matching results, if in the long-distance or add 120 kohm will be very harmful to the signal, because the can transceiver drive capacity is certain, transmitted 5 km, back to the route impedance (canh+ CANL) is nearly 250 kohm, and if a 120 ohm resistor is added, the transceiver of the terminal receiving node can receive only about 1 volts. Such a voltage amplitude of the anti-jamming ability is very poor, the communication presents a good time bad phenomenon. Therefore, in the long-distance communication, the terminal resistor is recommended to add to 300 Euro-500 euro, can guarantee the signal amplitude above 1.2V.

In fact, we put the oscilloscope on the terminal node to see, the most remote sent over the waveform is always closer than the oscilloscope issued waveform, a big cut. Without terminating resistors, you see a great "overshoot" at the edge of the signal, which is the signal reflection. Added 120 euro, then found that the far end of the waveform is shorter, but "overshoot" is also a lot smaller. The addition of 300-500 euros, you can ensure that the far end of the waveform is not short, and "overshoot" is not big.