Questions tagged [can]

CAN stands for Controller Area Network and is a bus often used in automotive applications. It is a two-wire differential protocol and works on baud rates from 10 kbits/sec to 1 Mbits/sec.

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33
votes
3answers
141k views

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

I know the reasons for using terminating resistors on a CAN bus and how important it is. But why 120 ohm? How did this value come up? Is there any specific reason to use 120 ohm?
48
votes
5answers
33k views

Is a CAN enabled microcontroller sufficient to drive a CAN bus?

There are a number of CAN modules built into microcontrollers these days. The PIC18F2480 is an example of that. Is that microcontroller (with built-in CAN) capable of driving a CAN bus on its own or ...
8
votes
2answers
4k views

CAN Transmission and termination resistors

I have been trying to set up a CAN network using PIC18F25K80 microcontrollers and an MCP2551 to communicate between them. Can I use two simple wires as a CAN bus by just connecting the CANL, CANH of ...
2
votes
5answers
8k views

STM32 HAL_CAN_Transmit always returns TIMEOUT (HAL_CAN_STATE_TIMEOUT)

Setup I am using an STM32F103C8T6 (aka Blue Pill). With the STM32Cube I set CAN_RX to PB8 and CAN_TX9 to PB9 (these are defaults/nonchangeable). Circuit simulate this circuit – Schematic ...
2
votes
2answers
6k views

How to calculate bus load of CAN bus?

I have a few questions regarding CAN bus load Is there any derived equation/formula to calculate the bus load? I need transmit below frames(Assume Standard frame format) at baud rate 500 kbps on the ...
2
votes
2answers
5k views

Difference between buffer and mailbox

Peripherals in Micro-controllers usually provide a way for us to send and receive data from it. Usually this are memory mapped registers. I have come across few terminologies. The most often used one ...
2
votes
0answers
664 views

Bus interface for short distances, many device data exchange - CAN, RS485? + characteristic impedance and media capacitance

I ran into some troubles trying to design a wired bus which will connect in about 64 testing devices. My first choice of mind was CAN bus, known of it's reliability and low EMC interference. However, ...
1
vote
1answer
475 views

Same priority for masters in a CAN network

I'm aware that messages on the CAN network are assigned priorities. I'm working on a 2oo3 voting system, and if each of the messages by the three masters are given three unique id's, I'll be making ...
21
votes
4answers
37k views

What's the maximum CAN bus frame (message) rate at 125 kbit/s?

My CAN bus is running at 125 kbit/s and is using extended frame format exclusively. I would like to know what's the maximum rate of CAN frame I can send out. Suppose the data length is always ...
13
votes
4answers
8k views

Implementing a CAN protocol layer in software

Background I'm developing a project which will require the modest microcontroller specs of: 8 12-bit, 10kHz ADCs 1kB of RAM 48-QFN or smaller footprint 20kbps daisy-chainable noise-resistant and ...
7
votes
3answers
2k views

GND difference between CAN nodes?

I am running a short (2 m) CAN bus with about 20 nodes. 1 Mbit/s speed, PIC 18F2580s and 18F4580s with MCP2551 transceivers, 10 MHz (with PLL to 40 MHz) crystal oscillators. Both ...
5
votes
3answers
11k views

CAN bus layout design

I am trying to design a CAN bus node. The CAN bus shall be split-terminated with 120Ohm, 60Ohm for each line. Therefore i tried using this paper to calculate a characteristic impedance of 60Ohm for a ...
9
votes
1answer
7k views

Significant differences between CAN and RS485 regarding the physical layer

In comparing the physical layer of CAN and RS485, I am trying to find the advantages of either one over the other. I found out that they are quite similar. Both are good in terms of common mode ...
8
votes
3answers
6k views

Why won't my CAN transceiver receive messages unless there is a long startup delay or a bus analyzer connected?

I am using a 16-bit MCU, PIC24HJ64GP504, to write a CAN based application. Basically it is communication between my board and one another node which continuously keeps on sending data to my board ...
2
votes
1answer
1k views

CAN bus goes through periods of re-sending messages continually

I'm having an issue where my microprocessor CAN bus module continuously re-sends its last message, even though it seems to be received properly by my USB-CAN monitor on the other end. I'm attempting ...
2
votes
4answers
3k views

CAN Initialization Timeout Error in STM32F4

I am using an STM32F446ZET6U Nucleo Board (programmed with CubeMx and Keil uVision 5) and I try to use some of the ST's examples in order to learn about its peripherals. I am stuck with the CAN ...
2
votes
3answers
617 views

Wired sensor network

We are trying to develop a wired sensing network that will have up to 200 sensors attached to it, spread over what could be 100 m. There will be one main controller that uploads each sensor's ...
1
vote
1answer
508 views

CAN bus connector issue

I've got a circuit with a CAN bus connector like the following with two RJ11 connectors to be connected in a daisy-chain style: But only one of them is working (I tested them by connecting to ...
1
vote
1answer
936 views

Current Consumption of CANbus (CANH and CANL)

I'm looking to use the SN65HVD230 CAN transceiver but had a question about the current consumption. Datasheet: http://www.ti.com/lit/ds/symlink/sn65hvd230.pdf In table 8.3 Recommended Operating ...
0
votes
1answer
680 views

PCB Routing of CANH and CANL

Continuation from an earlier question: Current Consumption of CANbus (CANH and CANL) I understand how to specify my power supply for multiple CAN transceivers but I am now wondering about the details ...
8
votes
1answer
2k views

Effect of splices on 120 Ω twisted pair cable impedance a.k.a correct way to attach stubs to the bus?

I am currently in the process of designing a wiring loom for a race car control system which must also connect a number of devices via a CAN bus. This is my first encounter with CAN bus (J1939-15) ...
5
votes
2answers
2k views

How do I program 2 CAN nodes to transmit continuously in succession?

Suppose I have three CAN nodes: A, B and C. We know that when two nodes transmit at the same time, the node that has the least SID will prevail over the bus and the other node will have to give the ...
4
votes
5answers
15k views

CAN Bus Physical Layer Twisted pair or not

CAN bus is very common in automotive or vehicular applications. In our case, we are using aerial platforms with have CAN bus links between operator remote and ground control box. As is very typical ...
4
votes
1answer
2k views

Switching a resistor by software

I want to communicate with a microcontroller over a CAN bus which needs (ideally) 120 ohm terminal resistors at the end of each bus. I want to integrate this resistor into the circuit and activate it ...
3
votes
1answer
762 views

How can CAN transceivers ouput CANH=3.5V and CANL=1.5V?

When sending a dominant bit (0bit) on the CAN bus, I understand that CAN transceivers output CANH=3.5V and CANL=1.5V. But when looking at the schematics of a CAN transceiver, I do not understand how ...
2
votes
1answer
1k views

MCP2515, CAN bus, and transmission failure

I'm trying to interface with a GPS device that is intended to connect with a vehicle via the CAN bus. I'm using an MCP2515, driven via SPI by a Parallax Propeller project board. I've successfully been ...
1
vote
1answer
1k views

Why is the CAN bus always busy (microcontroller)?

I'm trying without success to perform CAN bus communication between an microcontroller and the host (my computer). My question does not depend on the microcontroller, but on the CAN Bus (classic CAN). ...
11
votes
5answers
22k views

What is the color code for CAN Bus?

I would like to know if there is any color code specified for CAN Bus communication wiring, maybe in ISO-11898-1? (I have no free access to the file) I looked for any official documents without any ...
6
votes
4answers
3k views

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

I know you need to terminate the 'ends' on a high speed CAN bus but what if you know nothing about the topology of the network or where the bus will go. For my application i have designed a data ...
4
votes
3answers
898 views

CAN bus termination in a fully modular design

I am trying to make a fully modular festo cube design that is controlled with a CAN bus, but I am trying to figure out where to terminate the bus. I am even not really sure if what I am trying to do ...
4
votes
1answer
10k views

Is it possible to have any CAN baudrate?

Is it possible to have any CAN baud values? e.g. 507 baud If not, on what basis is the standard values are derived?
4
votes
1answer
33k views

Controller Area Network (CAN), high speed and low speed

Is the difference between high- and low-speed CAN only with respect to baud rate values? Is the CAN transceiver programmable for a range of speeds or is it fixed for a specific value? For example, can ...
3
votes
2answers
248 views

CAN bus TX failing in a strange way

I have been trying to pass CAN frames between two different CAN busses using two different CAN channels on a STM32F746 MCU. The system always fails and freezes up in TX when it is supposed to be ...
2
votes
1answer
822 views

Electronically connecting/disconnecting device from a CAN bus

What I'm trying to do can be best described by the following circuit based on an electromechanical relay: simulate this circuit – Schematic created using CircuitLab However, is there a simpler ...
2
votes
2answers
233 views

Isolated CAN transceivers as a CAN bus extender

I am designing a system to 'hack' into a CAN bus. My first idea was to split the target CAN bus, terminating both ends into isolated CAN transceivers, and use a MCU to pass packets between the buses ...
2
votes
0answers
77 views

Interoperability between regular and single-wire CAN bus

Is it possible to connect a regular CAN transceiver (ISO 11898-1) to a single-wire CAN bus (SAE J2411) in a compatible way? By "compatible" I mean that the whole system should support valid J2411 bus ...
1
vote
4answers
210 views

CAN bus communication mechanism

Does every node on a CAN bus just keep transmitting data no matter what or does it only transmit data when it is "requested" to by other nodes on the same bus?
1
vote
1answer
93 views

NAK in CAN bus for STM32F3 uC

I have a problem with the NAK on the CAN bus. On STM32F303RE I wrote a code for communication via CAN bus with car dashboard (Instrument Panel Cluster). The communication works, I manage to receive ...
1
vote
1answer
320 views

Does CANbus need to be isolated?

In my design - rugged computer - I have connected the digital gnd to the isolated CANbus gnd by mistake. Does the CANbus standard state that it has to be isolated? Can that connection harm the CANbus?...
1
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2answers
6k views

Reading from CAN bus of a Chevrolet Cruze using an Arduino Uno

I'm using the Arduino Uno, CAN bus shield, and OBDII to DB9 Cable using their provided libraries. I was only able to initialize it. Readings: While connected to the car: CAN-High: 2.7 V - 3.0&...
0
votes
2answers
3k views

Eagle library for MCP2551

I need to make a PCB, and the only software I have is EAGLE. All the other parts are listed in my libraries, but where can I find a library that has MCP2551 (CAN transceiver)?
0
votes
3answers
324 views

Can I use this analog switch for CAN bus signals?

In the deutsch 9 pin obd interface for heavy trucks, some manufacturers use the pin F,G for J1939 protocol and some use it for J1708 protocol. I am trying to use a NLAS4684 analog switch with dual ...
0
votes
2answers
103 views

Can we implement physical DIP switches to route different differential signals?

I want to route two different CAN BUS signals (differential) to a CAN controller. Since the controller has only one CAN interface, I can not connect both differential CAN signals to the input of the ...
0
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0answers
232 views

Some questions about CAN transceivers

I bought different type of CAN transceivers: Two with an CJMCU2551 (left in the picture below). and four with TJA1050 (right in the picture below). CJMCU2551 (left) has pins: VCC, GND, CTX, CRX, CANH,...
0
votes
2answers
3k views

What is the maximum bitrate supported in the Can Bus?

i began reading about Can Bus for my final year project i have to send a file to be flashed into the microcontroller using the CAN BUS . I have found that the maximum bitRate that can be achieved is ...
0
votes
3answers
205 views

CAN Bus first steps

In a few months, I will need to build a project that will let me connect from my PC to a power supply via CAN bus. I don't have this power supply here and have zero knowledge (even less) of how to do ...