Actually I was inspired from this design: https://www.ti.com/tool/TIDA-00527 I think you should look at this.I'm not at all surprised that you are having problems. This is perhaps the stupidest design I have ever seen. How do you expect the CAN transceiver to drive all of that capacitance, transceivers, and the distributed capacitance of the cable besides? There is no accounting for transmitter drive levels or receiver thresholds. You are way better off running a separate data pair and power pair and using the network to power just the transceivers. Use freaking DeviceNet cable -- it was designed for this purpose, and can support in excess of 32 nodes at 500 kbits/sec. It betrays an incredible ignorance of how the CAN physical layer is supposed to operate. Oh and lose the slope control it is just about the most useless of features.
Puttining optional termination resistors on a device is a foolish thing to do. It will definitely bite you when you go to install these devices and you can't quickly decide which devices have them and which ones don't when things don't work. Terminations BELONG on the cable system, and nowhere else.
Just as an exercise, tell me what the input impedance of 32 transceivers, all connected in parallel is?
TI says they are doing site maintenance and that info is inaccessible. Why don't you give me the executive summary and we'll go from there. I have no reason to doubt your intentions. I think you just stumbled into the wrong pathway.Actually I was inspired from this design: https://www.ti.com/tool/TIDA-00527 I think you should look at this.
"You are way better off running a separate data pair and power pair and using the network to power just the transceivers. "
This is not the design I planned.
I think when you examine the sample design(TIDA-00527) you will understand why I tried something like this.
I know the problem I'm talking about is impedance.
I just need different opinions.
Also after I put termination resistor on all nodes, data transfer achieved from all nodes(5nodes), R56 and R60 are not optional.
Like I said the TS needs to study CAN and the reasons for the design decisions in more detail. It seems fairly clear that he is lacking in that regard.There a very important difference between RS485 and CAN. RS485 has push-pull drivers, CAN doesn't, it drives each line one way only, with a resistor to return it to the centre point, so your peak-to-peak signal is much smaller.
Note that the TI app note requires data with no net Dc, and suggests Manchester coding.
CAN with Manchester coding???
CAN always has net DC , and also could transmit no power when it is in the recessive state.
Really, you’re not on to a winner.
If you've only got two wires and ground, how about single-ended CAN or LINbus instead?
Hi again,TI says they are doing site maintenance and that info is inaccessible. Why don't you give me the executive summary and we'll go from there. I have no reason to doubt your intentions. I think you just stumbled into the wrong pathway.
BTW -- what bitrate are you using, what crystal are you using, where is the sample point and what is the SJW?
Thanks for your return, we don't use schottky diodes,It will be completely canceled in the next revision.I think it's a matter of scale - one master isn't going to power 32 slaves, each of which powers a microcontroller taking 30mA or so, but powering one or two low-power slaves is a different matter.
Also, whether or not the slave transmits is a big factor. It has to drive 40mA (5V/120ohms) when there is no power coming in.
In fact, all the time the master is high-impedance (i.e. waiting for a slave to transmit) there is no power being supplied to the slaves.
CAN makes the situation worse - power is only available during a message when a zero is being transmitted (so, about half the time) and not at all between messages. A typical CAN transceiver can use as much as 2.5mA in quiescent state.
The CAN driver peak output voltage into a double-terminate load is 3V, after that goes through two schottky diodes, there's not even enough voltage to power a CAN transceiver. Even if that problem can be overcome, the terminated line takes 50mA leaving only 30mA to supply external loads. Assuming 50% ones:zeroes, that's down to 15mA, and assuming the POWERED node only transmits 50% of the time, it's now down to 7.5mA, that's three transceivers that don't ever transmit, and no power left over for any other circuitry.
I still think the idea of power-over-CAN isn't going to fly.
We had this problem in our first attempt, so we removed the diodes, now it can be thought as if there is 0 ohm instead of diodes.But now you have D5-D8, which will drop about half a volt if they are schottkies. So the remaining power supply, if you start with a 3V p/p signal from the CAN driver, is now only 2.5V. Not enough to supply a CAN transceiver.
You are asking to be given a whole lot of valuable information that may actually belong to the TS employer. Certainly the concept of your product is interesting, but what I have seen of the workmanship of alarm system installers it is a poor choice to put everything into one loop, subject to failure due to poor installation. There may be exceptions but I have not seen them yet.Hi,
I'm Mohammad and I'm working on a same subject,
would you please tell me have you done it or not?
there is an addressable fire alarm system witch works in the same way and we are on way to create it,
so here is how it works:
we have a single loop witch can provides up to 255 detectors on just a "2 wire twisted pair" and I'm sure the protocol is CAN;
the current consumption of every detector when they are on standby mode is down to 20-100 uA and when they are activated they use like 5 mA.(and more interestingly they are non-polarity so the user can install it more easier).
it is done so it's not impossible
so any idea so you can help me( i really would be grateful).
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