Trio Motion 32-bit modbus

Hi guys!

Has anybody used Trio Motion's controller with a 32-bit modbus communication setup? They offer two types, IEEE floating point and 32-bit integer, but I'm having trouble with both.

Thanks!

TM

I havent used one, whats the problem you are having ?

It may be its just a Modbus issue rather than the controller, or have you used Modbus on projects before ?

Hi! What was so tragic about 1969?

Ah, but to the question: I've used modbus serial to transceive 16-bit integers between a Trio and a Unitronics V280 for a couple of years now, and it works just fine.

I would like to be able to transceive 32-bit numbers. Right now, for any value over 32xxx, I have to break it into 2 16-bit integers and reassemble it at the other end. This works, but it is wasteful of memory, time consuming, and makes my logic look fat.

Trio has come out with the announcement that they support IEEE floating point and 32-bit long integer over modbus now. Of course, neither is an official modbus standard, so it's a crapshoot regardless, but in my case, it's completely non-functional.

I have suspicion that this is a big/little-endian problem, but I was hoping to see if somebody else had used 32-bit trio modbus communications successfully, and could provide some tips, pointers, or cautions.

Thanks!

TM

Well we use Floating and 32 bit integers from a device with no problems, are they swapped for any reason ?

i.e. LSW,MSW instead of MSW,LSW as the PLC would expect (Least Significant Word, Most Significant Word)

TimothyMoulder said:

Right now, for any value over 32xxx, I have to break it into 2 16-bit integers and reassemble it at the other end. This works, but it is wasteful of memory,

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Duh, but it isn't wasteful if you need the resolution. We have made 16 bit motion controllers for a many years and took a lot of heat because we DID NOT support those wasteful 32 bit numbers.

time consuming, and makes my logic look fat.

Click to expand...

Yes, so? What did you expect when you have a 16 bit master and a 32 bit slave. You can see others have the same problems with our 32 bit controllers when interfacing to TI555s and the like.

Trio has come out with the announcement that they support IEEE floating point and 32-bit long integer over modbus now. Of course, neither is an official modbus standard, so it's a crapshoot regardless, but in my case, it's completely non-functional.

Click to expand...

It shouldn't be. The answer is obvious. Make your device compatible with a modicon PLC. Duh again. That is what we did. We have been compatible with all other devices that use Modbus like AD or micrologix. So Delta, Modicon, AD and Rockwell can get it right.

I have suspicion that this is a big/little-endian problem, but I was hoping to see if somebody else had used 32-bit trio modbus communications successfully, and could provide some tips, pointers, or cautions.

Click to expand...

Modbus uses a very screwy format for downloading 32 bit floats.
It is a combination of big and little endian. The words are sent low word first but the bytes within the word are high byte first.

Historical note, the early Modicons were bit sliced AMD 2900s and mimic a PDP11 which were big endian. Later Modicon switched to the current x86 microcontrollers which are little endian.

Note, both the DF1 and Modbus were written to serve an immediate purpose without thought of the future. Neither of these protocols gave any thought 32 bit numbers or making 16 bit numbers efficient. That is, words are not aligned on even byte boundaries and 32 bit numbers are not aligned on boundaries divisable by 4. This means the processor must often have to make two fetches just to read or write one word.

Hi Peter! Always good to hear from you

Peter Nachtwey said:

We have made 16 bit motion controllers for a many years and took a lot of heat because we DID NOT support those wasteful 32 bit numbers.

Click to expand...

I sense some bitterness. Seriously though, the Trio MC206x
(slave) is supposed to be a 32-bit controller, but for some hairball reason, they use 24-bit integers. It seems they've worked out a method in the OS to overcome this, and allow long integer communication. Nonetheless, it does not seem to be working with my comm setup.

I'm constructing a "sniffer" to hook into my serial communications and see if I can get to the bottom of this, but I was hoping somebody already had some info on Trio's peculiarities.

Peter Nachtwey said:

It shouldn't be. The answer is obvious. Make your device compatible with a modicon PLC. Duh again. That is what we did. We have been compatible with all other devices that use Modbus like AD or micrologix. So Delta, Modicon, AD and Rockwell can get it right.

Click to expand...

Yes... and no. As you point out yourself, Modbus was not developed with 32 integers in mind, so there was never a formalized standard. Keep in mind that everybody talks just dandy at the 16-bit level.

Like I said, I want to get some data at the transmission level and send it to the principles involved and maybe get something worked out.

Thanks!

TM

TimothyMoulder said:

I sense some bitterness.

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I am not bitter, I am just making fun of your whining about 32 bits. Most people prefer having 32 bit float rather than 16 bit INTs. I know I had customers asking for 32 bit float for years until we came out with our 3rd generation controllers.

I'm constructing a "sniffer" to hook into my serial communications and see if I can get to the bottom of this, but I was hoping somebody already had some info on Trio's peculiarities.

Click to expand...

We rarely need a sniffer. We just look at what was sent and what was received to see how the comm software rearranged the bytes. We use
http://babbage.cs.qc.edu/IEEE-754/32bit.html
http://babbage.cs.qc.edu/IEEE-754/Decimal.html
I don't know anything about Trio. I do know that we must solve the same problems.

I also know it is a crime that the Modbus standard hasn't been updated. This question gets asked a million times because there is not official standard. You know that winds up my integrator. The Modbus TCP standard is a little more complete.

If you do talk to the Trio guys, strongly suggest they make their controller capable of exchanging floats with a Modicon PLC

Hi Peter!

Thanks for the sites, I'll put those to good use

The 32-bit float thing seems kind of natural. And it is indeed a crime they've not updated the standard. All I can think of is, they are afraid of issuing something concrete and breaking 30% of the modbus devices in the world.

Peter Nachtwey said:

You know that winds up my integrator.

Click to expand...

LOL! Good to know your sense of humor is still intact

TM