topic Send Hex string over Modbus to SMC Actuator in Instrument Control (GPIB, Serial, VISA, IVI)

Send Hex string over Modbus to SMC Actuator

Lazer723 — Mon, 22 May 2023 14:33:51 GMT

Hi,

I am trying to send a hex string command to multiple holding registers via Modbus to an SMC traverse. I know I need to convert this string to a byte array, but I cant use the "string to byte array" VI because it interprets as ASCII.

I have attached the VI with the command inside, I need to pass it to Multiple Holding registers VI.

Thanks

Re: Send Hex string over Modbus to SMC Actuator

altenbach — Mon, 22 May 2023 14:49:31 GMT

What would happen if you would change the display format of your string constants to hex display (right-click) and re-enter your data? Similarly, formatting your number as hex is probably incorrect.

Re: Send Hex string over Modbus to SMC Actuator

Lazer723 — Mon, 22 May 2023 15:27:27 GMT

Hi,

I'm formatting as Hex initially because I want to be sure that I am sending the exact thing that is in the manual.

If I convert the string constant to Hex display and then paste the data in, what would I do with that output?

Also, The only part of the string that needs to be variable is the (3) Position input where 30000 (300.00 mm e.g) translates to 00 00 75 30.

Thank you for your help

EDIT: I see, now I can directly connect the hex string to the String to Byte array and it interprets it correctly. Can this Byte array then be directly sent to the Write Multiple Holding registers VI?

Re: Send Hex string over Modbus to SMC Actuator

altenbach — Mon, 22 May 2023 15:29:55 GMT

Sorry, I am currently not at a computer with LabVIEW, but there is a big difference between:

Hex formatted string, i.e. a string containing exclusively ASCII characters 0..F
A binary string where all values (0..255) are allowed and that looks correct if the display is set to hex display.

You want #2.

Re: Send Hex string over Modbus to SMC Actuator

Lazer723 — Mon, 22 May 2023 16:55:03 GMT

Hi,

i understand now. I think I have gotten it to be in the correct format. So the move command is in two steps, Step 3.1 is to write the move settings, and 3.2 is to initiate the move. I have attached a snippet. However, nothing is moving. I should mention that I know I am communicating with it correctly because I am able to Home it through boolean (coil) flags.

Re: Send Hex string over Modbus to SMC Actuator

altenbach — Mon, 22 May 2023 17:39:34 GMT

This is still a horrible mess.

Please show the display style for all string diagram constant.
Your uninitialized shift register will grow forever because it contain stale data. It should be U8, so wire the default tile
You probably want to cast the position, not format it.

Re: Send Hex string over Modbus to SMC Actuator

altenbach — Mon, 22 May 2023 18:02:42 GMT

See if this can give you some ideas....

Re: Send Hex string over Modbus to SMC Actuator

Lazer723 — Mon, 22 May 2023 19:10:59 GMT

Haha, I wish I could say it wasn't a horrible mess. Just trying to get a proof of concept before I start streamlining. Yes, your example makes a lot more sense. That will result in a 1D array of 8bit bytes, but the Input of the Write Multiple Holding Registers.vi says it normally accepts 1D of 16-bit words as the register values. The controller I am using runs on 8 bit length.

Would U8 still be correct?

Thanks a lot for your help

This snippet didn't result in any movement.

Re: Send Hex string over Modbus to SMC Actuator

altenbach — Mon, 22 May 2023 20:09:23 GMT

Well, you can cast the string to an U16 array equally well. Don't forget to calculate the checksum and append it.

I did not validate the rest of your strings, so check the manual.

Notice the red coercion dot at the IO function? If you hover over it with the mouse, what does it say it expects?

Re: Send Hex string over Modbus to SMC Actuator

Lazer723 — Wed, 24 May 2023 11:58:33 GMT

Working!!

So after much fiddling I've got it working. There were a few key things that needed to be known. The modbus Write Multiple Holding Registers.vi accepts only a 1D array of 16bit words (essentially two 8 bit bytes put together), simply casting my 8bit array to U16 would only pad each element with an extra 8 bits of zero, when what should be done is to combine each pair of 8 bits into a 16 bit word. So [11,22,33,44] would become [1122,3344] instead of [0011,0022,0033,0044].

I found it easier to go back to regular strings and loop Hex to 16bitNumber and form an array rather than reshaping the existing U8 array.

This works because the modbus VI actually does a lot of the heavy lifting, it splits each 16 bit word into two U8 bytes before sending it to the device. Also, I needed to remove any preamble to the hex string, (the number of words and number of data elements), and only give the exact values that are to be written to the registers, the modbus vi appends all necessary preamble, and indeed CRC bytes all by itself.

I found this out by opening up the modbus VIs and went digging.

So in the end here is the snippet that worked. Allowing me to set the speed and position and results in actuator motion. (All this is inside a larger VI that initialises the modbus master etc.)

Thank you for your help!

Re: Send Hex string over Modbus to SMC Actuator

altenbach — Wed, 24 May 2023 20:39:14 GMT

NO!!!! Just NO!!!!

This code is just plain ridiculous! Why format it in normal display in hex format with space delimiters using 3x more momory, just to strip it all out nanoseconds later.

Here's code that gives exactly the same output as yours!

(note the correct representation of the controls!)

You NEED to do a few tutorials and understand the difference between a hex formatted string using characters 0..F and a binary string where each character can be anything from 00 to FF). You also need to understand the display style of strings.

Also note that your FOR loop and shift register is just pure Rube Goldberg code! Compare the two alternatives:

I also strongly recommend to stay away from stacked sequences. There is a reason they are no longer in the palettes!

Re: Send Hex string over Modbus to SMC Actuator

Lazer723 — Wed, 24 May 2023 22:22:01 GMT

Ah yes. It seems I have a lot to learn about hex strings and 'text' strings and type casting in Labview!

Sorry, this is my first foray into digital types.

So if I understand correctly, finally, inputting the hex data into a hex-displayed string actually stores the data in binary (a binary string?) rather than ascii, which leaves it free to be easily reinterpreted into any desired numerical representation. And the Type cast block formats the input into the same hex displayed string (binary string?) that is connected to at the output. So the string concatenate block is now in binary string mode as soon as you wire a hex-string to it? Or is it in fact that everything is always in binary string mode but the 'regular' string just displays the binary in ascii. Still not used to the whole non-text string thing, but I think I'm getting there.

I was also not aware that the Hex to number vi works with arrays as well, that's pretty neat and definitely neutralises my loop.

Thanks for the code

Re: Send Hex string over Modbus to SMC Actuator

altenbach — Wed, 24 May 2023 22:29:23 GMT

The display style of a string is a purely cosmetic property and does not change the actual string data. But yes once a string is in hex display, it know what to do when you enter data.

Typecast just blindly does big endian and never generates errors. If you need more control, you can use "flatten to string.

A string is a string is a string. ASCII is just a convention how to interpret bit patterns to alphabetic characters.