High-performance SAE J software based protocol stack. Complete J source code is provided. Get on the Bus: J and J Vehicle Bus Standards on established protocols that vary based on vehicle manufacturer, vehicle model. J defines the physical layer, which are the hardware (wiring) and basic protocol that is needed for J and J to transmit messages.
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User Control Panel Log out. Forums Posts Latest Posts. Forum Themes Elegant Mobile. Essentials Only Full Version. If so, if the j protocol is on the rs physical layer, can the CAN be interface to the rs so it can interpret the j protocol??? Hi The Can controller area network on this forum is not a very successful topic I have also questions on this forum about Can It is just strange that not one of the microchip application Engineers get involved in this topic.
In all other treads i constanly see MC moderator input only at the Can nothing. Maybe that there is not that much interest in this topic??? This thread is a little old, but it doesn’t seem like anyone really answered the question, so I’ll give it a try. The CAN protocol is totally incompatible with J They are not related at all.
The basic problem is that the CAN specification defines certain requirements around the identifier, or the first part of the message. This includes bit stuffing at pre-defined intervals the transmitter adding bits that are not part of the message at all.
If this were not done properly, then the receiver would flag it as an error. Also, in CAN, part way through transmitting the message the transmitter releases the bus for 1 bit time and receiving nodes are supposed to send an ACK bit.
SAE J – Wikipedia
So even if you got past the bit-stuffing, the receiver could trash the message being sent, and would miss one of the bits. None of this is handled the same in J Also, the message length of J is variable up to 21 bytes for standard messages. The only indication of when the message is over is when the transmission stops. In CAN, the message length is defined as part of the identifier, and is a maximum of 8 bytes. So even if you got protoxol all the problems with the bit stuffing and ACK, there’s no way you could capture all the J data.
And that’s just the beginning. Now that I know more. The max length of any J is 21 bytes 10 bits per character. The messages are prioritized and one can both send and recieve. More correctly, request data. The resessive state is high, and dominante is low.
J1587 / J1708 Network Operation and Testing
This means that all the transmitting onto the J bus requires a logic inverter. However, it is not an RS physical layer, but a closly pritocol RS with some modification, any how it is common mode current loop and not a voltage driver. Hallo Thank you for the report back.
I have the same feeling about this forum, “no moderaters involved” there are so many questions about CAN. I think that not many eng. Its my major product, so I rely would like more people to look at this forum. I did not get any usefull response on my repeater question.
And you can not build a large canbus without repeaters. It is just strange that not one of the microchip application Engineers get involved in this topic. I only just saw this post. I would have to question the “all the other threads” comment. Posts from Microchips FAE’s are very few and far between. I’m afraid it is “users, help yourselves” here, and unfortunately, not many regular posters are working on CAN.
I also post at: Links to useful PIC information: Posting images, links and code – workaround for restrictions. There are numerous CAN forums on the web.
J | SAE J Software, Protocol Stack, Source Code
If you have a general CAN question that is probably a better place to look than here. This is a Microchip forum. Although I can answer some questions about CAN, I am by now means an expert and have only used it for about eight months.
I don’t blame microchip for not responding to the vast majority of these postings. Part of engineering is learning how to do research i1708 testing your own ideas.
Thanks to all for your reply. Since this post were made in January we also advaced great n1708 in CAN development and I must admit that Microchip Switzerland got on Board with us and supported us with Technical know how and advice.
J and CAN are seperate physical layers.
We have device drivers for both. If you have any questions, please contact us at http: SAE J and J are different on software and hardware. However, there are still something similiar: J is a multi-master network tooand it implemented the bus arbitration too, but different than the CAN hardware arbitration, J using j17708. For more info, please refer to our forum links: Debug breakpoints automatically disabled 16F88 cannot set internal oscillator frequency beyond Why does my PIC32 run slower than expected?