Checksum

[HughQuinn]

I have a an output of a Mass Flow Controller and have the entire string figured out except for the checksum. Here is the output ff ff ff ff 82 8a 32 7c 8d 2c ec 05 39 00 00 00 00 37 00   the checksum is 37 00 no idea how they got that by using an exclusive or process and Im pretty sure it starts at the 82

[Donald]

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@hhhhhhhhh wrote:

... Here is the output

ff ff ff ff 82 8a 32 7c 8d 2c ec 05 39 00 00 00 00 37 00  

the checksum is 37 00 no idea how they got that by using an exclusive or process and Im pretty sure it starts at the 82

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hhhhhhhhhhh,

xor gives 0x37 as shown in the attachment.

[PlasmaGuy]

Wow - that picture is worth a thousand words.  I'm trying to do something similar with a Mass Flower Controller (essentially trying to write my own - somewhat simplified - serial interface).  I spent the entire day yesterday and came up with about 5 different ways of calculating XOR checksum that didn't work.  This way looks nice and simple.

For the MFC I'm working with, you need to ignore the preamble "FF FF" when calculating the checksum.  I'm not worried about looking at the checksum of replies coming from the MFC (perhaps I should be?) since I plan on simply extracting the relevant part of the string and the accuracy of the data isn't a life or death situation.  My trouble comes when I would like to calculate checksums on the fly as I send new set point commands to the MFC - so I will have to calculate them and then append them to the command string.

One question though:  what do you wire to the count input of the For Loop?  Is it simply the string length?


thanks,


PG

[Donald]

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@PlasmaGuy wrote:
...

One question though:  what do you wire to the count input of the For Loop?  Is it simply the string length?

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Plasma,

Nothing needs to be wired to the count input.  Indexing is enabled on the U8 array input to the loop and the size of the array controls the iteration count.  Good luck.

[HughQuinn]

If you are using Brooks Mass Flow Controllers I have developed software that takes care of all of that. It sets a set point for you and also reads the set point back through LabView and skips that SmartDDE and smartcontrol garbage.

[PlasmaGuy]

Many thanks, Donald.  That's good to know.  I will try this out and see how it works.


hhhhhhhhhh:  The MFC I'm using is a Burkert 8626.  Burkert has software that can be downloaded from their website that will give access to various parameters, but it's too clunky for my needs.  I need the ability to quickly switch between 3 states:  off, set point 1, set point 2.  The only way to change set points seems to be to type them into the software directly - and the problem is compounded by the fact that I want to control 3 MFCs at once.  I have to have 3 instances of the software running to do this as far as I can tell.

But all of this may be a moot point.  I discovered this morning that the 8626's have analog inputs (the documentation made it appear to be RS-232 only) for sending set points.  This would simplify the Labview program a bit, but I will have to by a new DAQ card with more analog outs.

I'm still determined to finish the serial communication method though, since it seems like a great programming exercise.


PG

[ali26]

salut tous le monde,
 
 voila, je suis la programme d'un masse flow controller sous labview, et je suis un peu bloque, je n'ai pas de driver de l'instrument, mais par contre j'ai les instructions. communication baser message.
 
 merci

[ali26]

hello,

I used the labview to order the instrument "mass flow controller", and I don't have the driver, but I have the instructions, and I I made this chart of labview, but I need help because the issu was the checksum out of read.vi

[Nitin_T]

Hi ali26

I was wondering if you could furnish some more details about the problems you are having. Presently, I can infer that you are having issues with checksum. Is this similar to the problem "hhhhhhhhh" was facing (see earlier part of this thread)? If not, please do let us know what is different or new? What kind of Mass Flow Controller do you have? What version of LabVIEW and VISA are you using? What type of serial communication are you using? Thank you.

[gotgot]

I used  Labview version 8.2, and the MFC 8100 series unit of celerity. I also used the RS485 serial communication. and the issue was that I anly have the instructions of the RS485 communication Protocol of Digital MFC Interface.

thank you for you response "merci pour votre aide"