How Low Resistance Affects CAN Bus Communication and Performance

Low resistance in your CAN bus can make big problems. You may see voltage drops. You may get signal errors. Sometimes, you can lose data. Hardware can break. The network can become unstable after these problems.

• Good resistance helps your system stay safe and work well.

  Always check resistance in your CAN network. This helps you avoid expensive problems.

Key Takeaways

• Keep the resistance at 120 ohms in your CAN bus. This helps stop signal mistakes and stops data from getting lost.

• Put termination resistors at both ends of the CAN bus. This matches impedance and makes signals better.

• Check resistance often to find problems early. This helps you avoid expensive fixes.

• Low resistance can make things get too hot and break hardware. Fix resistance problems fast.

• Use good habits like twisted-pair cables and strong connectors. This makes the network work better and stay stable.

Low Resistance in CAN Bus

Role of Resistance

It is important to know why resistance matters in your CAN bus. The normal resistance value for a CAN bus is 120 ohms. This value helps stop interference and lets signals fade fast. When you use the right resistance, your CAN network can switch to the recessive state quickly. This makes every signal better.

If you use low resistance, you can have problems. The bus might not match the cable’s impedance. Signals can bounce back and cause confusion. You might see voltage drops and unstable levels. Your CAN system can lose data or send errors. Hardware can break if this keeps happening.

Here is what good resistance does for your CAN bus:

• Matches the cable’s impedance (usually 120 ohms)

• Stops signals from bouncing and ringing

• Helps block interference

• Keeps bus levels steady for correct logic

Low resistance can cause impedance mismatches. Signals bounce back to where they started. These bounces can mess up signals and cause timing errors. You might see data get messed up or the system not work right.

Signal Integrity

Signal integrity means your CAN bus sends clear and correct data. Terminal resistors are very important. They stop signals from bouncing and mixing with new ones. When you use the right resistance, your network stays steady and your data is safe.

A termination resistor goes at each end of the CAN bus. It matches the cable’s impedance. If you do not use the right resistor, signals bounce and make voltage levels unstable. This can cause communication errors.

Low resistance can make your CAN bus pick up more noise. You might see more errors and lost data. Terminal resistors match impedance and stop bounces. This helps your CAN network work well.

Communication Issues

Data Errors

When resistance is too low in your CAN bus, many problems can happen. Low resistance makes voltage drop. This makes signals weak and hard to read. You might see more data errors. Your network may not send or get messages right.

Here are some common data errors you might see:

• Bit errors happen when the CAN bus tries to send a recessive bit, but the receiver gets a dominant bit instead.

• ACK errors show up when the transmitter and receiver do not match their baud rates.

• Bit stuffing errors happen if there are six dominant bits in a row.

• Form errors happen when the transmitter sends error flags because of ACK errors.

Data errors go up when resistance drops below 60 ohms. This can happen if you add too many terminators or if a short circuit happens. You might lose data or see mixed-up messages. Voltage drops make these errors worse. Your network can stop working well. You may need to check your CAN bus often to find these problems early.

Tip: If you see lots of data errors, check the termination resistors first. Fixing resistance can solve many communication problems.

Low resistance also makes more current flow. This can make parts of your CAN bus too hot. Overheating can break hardware and cause more data errors. You might lose important messages. Your network may disconnect at random times.

Network Instability

Low resistance can also make your network unstable. You may see voltage drops on the bus. These drops make signals weak and not steady. Your network can start acting strange.

You might notice these signs of network instability:

• Error frames show up more often.

• Communication errors happen during normal use.

• Signals become mixed up and hard to read.

• Signal reflections bounce back because of wrong termination resistance.

• Messages get messed up and lost.

Other signs are energy bouncing back at the end of the bus. You may hear weird random noise on the line. Sometimes, you see quick pulses that look like binary signals but have the wrong voltage.

Low resistance makes more current flow on the bus. This can cause voltage drops and make the network unstable. Your CAN bus may disconnect or lose messages. Hardware can break if the network stays unstable for too long.

Note: Stable resistance keeps your network safe. Always use the right termination resistors to stop voltage drops and errors.

Performance Impact

Error Rates

When resistance is too low, you will see more errors. The CAN bus needs the right resistance to keep signals strong. If resistance is low, signals can get weak or mixed up. Devices may have trouble reading messages. You might notice more bit errors or lost messages. Sometimes, the same message gets sent again and again.

Here are some ways low resistance can cause more errors:

• Signals get weaker and are hard to see.

• Devices might read the wrong bit value.

• The bus may send the same message many times.

• Error counters in devices can fill up quickly.

If you notice lots of errors, check your termination resistors. Fixing resistance can lower errors and help your network work better.

System Reliability

System reliability gets worse without the right termination. Your CAN network can become unstable. Devices might disconnect or stop working. You could see random resets or lost data. The whole system might slow down or even stop.

Low resistance also lets more electromagnetic interference (EMI) in. EMI is noise from other wires or devices. If your CAN bus does not have the right resistance, this noise can get into your signals. Devices might read wrong values or miss messages.

You can use this table to see how resistance changes system reliability:

Resistance Value	Error Rate	EMI Susceptibility	System Reliability
120 ohms	Low	Low	High
60 ohms	High	High	Low
No termination	Very High	Very High	Very Low

Tip: Always use the right termination at both ends of your CAN bus. This keeps your network stable and helps it work well.

If you want your system to last, check resistance often. Good termination helps your CAN bus block noise and keeps data safe. You will see fewer errors and better performance.

Diagnosis and Solutions

Symptoms

You can find low resistance problems by looking for some signs. Sometimes, devices turn on but do not send messages. You might see low voltage or resistance to ground. This can mean something is broken. Here is a table with common symptoms and what you might measure:

Symptom Description	Voltage/Resistance Measurement
Low voltage showing possible failure	1.4VDC or less
Device on but not sending messages	2.50 VDC
Resistance to ground shows damage	10K ohm or less

If you see these signs, your network may have trouble sending or getting data. You could notice random disconnects or error frames.

Detection Methods

There are a few steps to find low resistance in your CAN system. First, turn off the power. Use a multimeter to check resistance between CAN-High and CAN-Low. The number should be close to 60 ohms if you have two 120-ohm resistors. Check the terminal resistor for about 120 ohms. After you reconnect, measure again. The value should stay between 117 and 123 ohms. Test each CAN line to ground. You should see thousands of ohms. If the number is lower, you might have a short or broken part.

Here is an easy checklist for finding problems:

1. Take out the battery before you start.

2. Find a CAN point using the diagram.

3. Measure resistance between CAN-H and CAN-L.

4. Check the terminal resistor value.

5. Check resistance again after reconnecting.

6. Test for shorts to ground.

7. Measure from other points to find the problem.

You can also check voltages. Measure between CAN HI and ground (2.5–3.0Vdc) and CAN LOW and ground (2.0–2.5Vdc). If the numbers are not in these ranges, there could be a problem.

Best Practices

You can stop low resistance problems by following some good steps. Use twisted-pair cables to block noise. Make sure you have good grounding to keep things steady. Always use the right termination value, which is 120 ohms, at both ends of the main loop. Check wires with a multimeter and look at connectors often. Test voltage levels to make sure things work right. Pick good quality parts and connectors for your CAN bus. Check your system often to find problems early. Keep the area safe to protect your network from losing signals.

Tip: Good care and the right termination keep your CAN bus safe and working well. Checking often helps you avoid big repairs and lost time.

Low resistance in your CAN bus can make signals bounce back. This can cause data errors. Sometimes, communication gets slow or stops working. If you do not use the right termination, these problems get worse. Always put 120Ω resistors at both ends of the bus. Follow ISO 11898-2 rules. Run your wires side by side to keep the network strong.

• Test your system many times.

• Pick cables and connectors that fit your needs.

• Fix any issues early so things do not break.

Problem	What Happens
Signal Reflections	Signals get messed up
Intermittent Errors	Communication is not steady
Total Failure	The system will not work

Checking your system often and making good design choices helps your CAN bus stay strong, even when things get hard.

 

 

 

 

 

Written by Jack Elliott from AIChipLink.

 

AIChipLink, one of the fastest-growing global independent electronic   components distributors in the world, offers millions of products from thousands of manufacturers, and many of our in-stock parts is available to ship same day.

 

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