How to use 'read_multi_vars()' when variables is more than 20?

[su600]

Hi!
I have a problem when variables more than 20 in read_multi_vars(data_items)

snap7.snap7exceptions.Snap7Exception: b'CLI : too may items (>20) in multi read/write'

So I try to read variables by groups(each group have 20 variables) use read_multi_vars(data_items[0:20]), but there also has an error:

TypeError: byref() argument must be a ctypes instance, not 'list'

When print the type below：

print(type(data_items))
print(type(data_items[2]))
print(type(data_items[0:20]))

Got:

<class '__main__.S7DataItem_Array_48'>
<class 'snap7.snap7types.S7DataItem'>
<class 'list'>

Which means date_item[0:20] return a list, so what should I do to read more than 20 variables ?

Could you please help me to solve this problem, thank you!

[spreeker]

My solution was to put all my variables in a single huge DB-block and just every second or so read the entire thing in python using the read_db functions.. Did 500+ variables this way, so basically the entire PLC content. How about doing multiple calls? Stephan. Senior Software Engineer. +31 6 24 69 22 97 https://gitlab.com/spreeker/ https://github.com/spreeker/ https://www.nlx.io/ https://commondatafactory.nl/

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On Fri, May 8, 2020 at 9:58 AM Su600 ***@***.***> wrote: Hi! I have a problem when variables more than 20 in read_multi_vars(data_items) snap7.snap7exceptions.Snap7Exception: b'CLI : too may items (>20) in multi read/write' So I try to read variables by groups(each group have 20 variables) use read_multi_vars(data_items[0:20]), but there also has an error: TypeError: byref() argument must be a ctypes instance, not 'list' When print the type below： print(type(data_items)) print(type(data_items[2])) print(type(data_items[0:20])) Got: <class '__main__.S7DataItem_Array_48'> <class 'snap7.snap7types.S7DataItem'> <class 'list'> Which means date_item[0:20] return a list, so what should I do to read more than 20 variables ? Could you please help me to solve this problem, thank you! — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#155>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAOSMJ2IJ5FN4CTEU6VCH3RQO3SFANCNFSM4M37D6ZA> .

[su600]

@spreeker
Thanks for your solution, I'll consider this solution later.

Your solution may have to do some reprogram in the PLC, my application is more focus on connecting to an old PLC without program changed, which may not suitable very much.

I think Multiple calls is same as what I mean read by group, I also done this in PyLogix for Rockwell Allen Bradley PLCs. The key problem in this issue is how to slice the S7DataItem_Array and retain the datetype.

Thank you again, I'll continue try to find a solution.

[gijzelaerr]

Since there has been no activity on this issue I consider the question answered and will close this issue.