Xantrex XW6048 Reliability

Re: Xantrex XW6048 Reliability

more from up on the mountain.

"Xanbus has never been based on RS485 hardware. CANbus has its own hardware layer.

The XW Gateway communicates to the XW system components via Xanbus, and it makes that information available to the outside world through different Comm protocols. One of the options is to access the data through the Gateway's RS485 port which supports the Modbus protocol. To do this the WiPort on the Gateway needs to be removed. "

Re: Xantrex XW6048 Reliability

All I am thinking about is that it is Friday. Burnaby said to let you think about it...

Re: Xantrex XW6048 Reliability

boB wrote: »

Thanks Dave ! Now I see !. (I think I do anyway)
OK, so what they're saying is that "Xanbus" is still a CAN derivative and MODBUS is a separate method of interfacing with their gateway. I wonder why they went to all that trouble to do the work to make the modbus protocol ? What is it supposed to talk with ?? Supposedly, they did not want anyone to control their devices with the modbus.... Just monitor I guess.

Maybe it was designed for some special customer ?

boB

CAN Bus is a multi-master bus -- which is a large part of the performance problems. In a single-master bus, the master knows when it's going to talk, so collisions don't happen and there's no arbitration. In a multi-master bus, it's possible for two masters to start talking at the same time. They have to detect the collision, decide which has priority, then the lower priority device has to shut up and listen, and try again when the bus is idle. The more devices on the bus, the greater the probability for collisions.

Modbus =can= do multi-master, but a message to tell the current master to shut up would have to be sent by a slave so the "master" can turn around and become a slave. My recollection is that SMA's RS-485 / Modbus interface works this way -- a monitoring device starts off as Master, discovers the devices, then turns around and acts as a slave and snoops the bus while something else acts as master and drives the traffic needed for the monitoring device (and the rest of the devices) to get the data it requires.

Re: Xantrex XW6048 Reliability

boB wrote: »

CANbus physical layer and RS-485 are very similar. Beyond that, I don't really care about CANbus or its protocol very much.

No need for it ~YET~ anyway.

boB

Well ... they are similar in that they use electricity, but RS-485 reverses the polarity between D+ and D-.

In my experience, buses based on differential signaling are far more robust than single ended. With UTP wiring, any voltage induced into D+ is also induced into D-, keeping the voltage relationship the same.

Since CAN bus is single ended, any electromagnetic noise that induces a voltage into the data wire will cause a bit to be added or lost. And power generating gear is a very noisy EM environment. Which, in my half-baked opinion, is why Xanbus is cr@p.

Re: Xantrex XW6048 Reliability

boB wrote: »

Noise susceptibility to EMI is not always guaranteed. Noise immunity is not always guaranteed either of course for a bus with high CMRR.

CAN bus CAN be single ended, but CAN bus is first a protocol and not necessarily a physical layer definition. However, CAN bus has from my recollection mainly been implemented as a differential mode signalling system.

I thought someone posted that Xanbus was single ended? Obviously CAN can be implemented on top of just about anything (IP has been implemented using carrier pigeons, after all ...), but if Xantrex went with a single-ended solution and untwisted telco wiring parts (my recollection, the last time I was face-to-face with a Xantrex system), that would explain a lot. If it really is differential, I'm at a loss, other than CAN bus having issues with excessive traffic and collisions. Which seems to be the problem, based on my experiences (and those of others).

Doesn't really matter to me as I said. I'm not making car, truck or vehicle systems and the protocol is not all that inviting to me. It's "OK" I guess. About 11 years ago, at Xantrex, they were talking about Xanbus possibly being like CAN bus. Didn't excite me then either.

boB

The motor, battery and instrument controllers in my motorcycle (Vectrix VX1) talk among themselves using CAN. That's more than enough extra CAN bus in my life ...

Re: Xantrex XW6048 Reliability

SG,

From what I've seen, "too chatty" is definitely a large part of the problem.