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23 votes

What is the limiting factor for a CAN bus to exceed 1Mbps bandwidth?

From Controller Area Network Physical Layer Requirements CAN is an open collector technology – the protocol could not work otherwise. This means that the recessive state of a CAN transceiver is not ...
21 votes
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Significant differences between CAN and RS485 regarding the physical layer

When comparing the physical layer only, CAN and RS-485 are similar in that they both use differential signaling. This gives them both good common mode noise immunity. The main difference is that RS-...
19 votes
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Microchip documentation does not label CAN buss pins on micro controller pinout diagram

The CAN pins do not have fixed pin assignments. Instead you are able to select which of the "Remappable Pins" you wish to use (RP0 through RP15). If you refer to page 180 of the datasheet, ...
18 votes
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Enable interrupt but no ISR

If there is no ISR defined, the location for the jump instruction in the interrupt vector will either be null, it may be a jump to an exception routine, it may jump to the beginning of the program, or ...
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17 votes
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CAN bus signal integrity

No. The differential signalling is performing as intended. No. As long as the "common mode voltage" does not exceed the ratings of the transceiver. And the maximum DC ratings, which for a CAN ...
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16 votes
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CAN Bus Licensing

It's included in the cost of the parts. It's a lot easier to collect money from a few IC makers than from every person who makes a product using those parts.
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16 votes
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How to deal with signed int overflows

Clearing up some misunderstandings will probably help. First, your data is a 16-bit value. There's no "overflows" and "actual data" -- the 16 bits are just divided into two 8-bit pieces (bytes). To ...
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15 votes
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Which STM32 is best for logging a CAN network?

The shortest CAN frame is 55 bit times, so in the very worst case situation with a completely saturated bus consisting of one data byte frames (which is not really realistic for a CAN bus with any ...
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13 votes
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Twisted pair impedance

Do some time domain reflectometry, a useful video to this process is probably one from w2aew. He shows it with a coax, but it should work with anything that has a somewhat consistent impedance. In ...
  • 6,441
13 votes

CAN Bus Licensing

If you are using a third-party CAN controller chip, then they will have paid the licensing fee. The original patents related to the way the controller worked, so the vendor requires a license in order ...
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12 votes
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CAN bus layout design

You are getting confused about the impedance. The type of CAN you are apparently using is implemented as twisted pair with roughly 120 Ω impedance. That is why there is a 120 Ω resistor ...
12 votes

Does it matter which 2 nodes on a CAN bus you terminate?

Each beginning has its end. This can't be answered, because the question is not correct. What you have is the transmission line - a twisted pair that has two ends, and that's the place where the ...
11 votes
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CAN bus test via loopback - possible or not?

All CAN hardware error checks are performed by hardware - the CAN controllers. A CAN node cannot ack itself, by design. It will not receive its own messages. CAN is meant to have at least two nodes ...
  • 16.6k
11 votes

Does it matter which 2 nodes on a CAN bus you terminate?

It doesn't matter which nodes are at the ends, but it does matter that the terminators are at each end. The bus is a transmission line. To keep edges from reflecting at the ends of the cable, the ...
11 votes

What is the color code for CAN Bus?

CAN does not have a formalized physical-layer specification for conductor colors, or things like connector type or pin-out. There are common practices (like using a 9-pin D-sub connector) but no ...
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11 votes
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The CAN bus in this vehicle has only one 120 ohm termination resistance. What problems would this provoke?

From a professional point of view, this is a critical problem. Missing termination will cause energy bouncing back at the end which isn't terminated. This could lead to strange random noise on the ...
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10 votes
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Using CAN bus tranceivers with custom data link layer

Many small and cheap microcontroller have CAN built in. Look at some of the PIC 18 with "8" in their part number. You only need to add the physical CAN transceiver, like a MCP2551. If you just want ...
10 votes
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CAN bus - Priority/collision

Funny that with so many correct answers, I still feel like something is amiss or not clear enough. Even most complete answer by @Nick does not correct some wrong assumptions in the question. So, I'll ...
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10 votes
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Why common-mode choke on differential-signal serial lines?

Wouldn't the common-mode noise simply be cancelled in the receiver? A lot of noise would be heavily cancelled in a differential receiver but, high frequency stuff can cause problems and, of course a ...
  • 419k
9 votes

Why does the CAN bus use a 120 ohm resistor as the terminating resistor and not any other value?

CAN Bus is a differential bus. Each differential pair of wire is a transmission line.Basically, the terminating resistor should match with the Characteristic Impedance of the transmission line to ...
9 votes

CAN bus - Priority/collision

First let's clarify something. CAN bus addressing works on message IDs. CAN bus itself doesn't have node IDs. (One could create a scheme for where some kind of node ID is a part of the message ID, ...
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8 votes
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Will this selectable CAN BUS termination circuit work?

It looks like it should work if you're not pushing the CAN bus to the limit. You can definitely turn on the LED with 3.3 V since the maximum LED voltage is 1.5 V. It needs about 5 mA, so you can ...
8 votes
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How and why is impedence matching done for a CAN bus?

The "terminators" of a CAN bus serve two purposes: They terminate the transmission line. The type of CAN you are referring to is intended to be implemented as a twisted pair. 120 Ω is roughly ...
8 votes
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Why are capacitors and resistors commonly used with CAN High & CAN Low lines?

ISO 15765-4 "Road vehicles — Diagnostics on Controller Area Networks (CAN) — Part 4: Requirements for emissions-related systems" section 8.4 relates to "External test equipment", a ...
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7 votes
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BeagleBone Black CAN bus setup

There is concept called device tree overlay and you can think of it as request for specific pin setup on the device itself. Some pins on the board are by default dedicated for specific purpose, SPI ...
7 votes

CAN bus layout design

You are knocking yourself out for no good reason. CANBus, with a 1 MHz maximum bit rate, is largely impervious to PCB termination issues. A few inches of mismatch on a PC board simply doesn't count in ...
7 votes

Only getting data when 'rubbing' wires

You need to connect three wires: CAN-H, CAN-L, and ground. The CAN lines are differential, but they are still ground-referenced. That's another way of saying that your CAN receiver probably has a ...
7 votes

What is the limiting factor for a CAN bus to exceed 1Mbps bandwidth?

It can. Meet CAN-FD. Why was a new protocol needed? CAN is a multi-master bus with arbitration and error reporting. These features limit the data rate based on the cable length, since it takes a ...
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7 votes
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Ethernet vs CAN bus physical signal

On a hardware level: The CAN bus works by a voltage differential between a pair of lines. The Ethernet bus is current-driven and is coupled through transformers at both ends, providing galvanic ...
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