# Problem writing variable to PLC Siemens S7 1500

**URL:** <https://forum.inductiveautomation.com/t/problem-writing-variable-to-plc-siemens-s7-1500/67376>\
**Category:** Ignition\
**Tags:** ignition81, vision\
**Created:** [December 8, 2022, 9:44am UTC](https://forum.inductiveautomation.com/t/problem-writing-variable-to-plc-siemens-s7-1500/67376 "2022-12-08T09:44:26Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![stefano.sforna](https://avatars.discourse-cdn.com/v4/letter/s/91b2a8/32.png) [@stefano.sforna](https://forum.inductiveautomation.com/u/stefano.sforna)\
**Post date:** [December 8, 2022, 9:44am UTC](https://forum.inductiveautomation.com/t/problem-writing-variable-to-plc-siemens-s7-1500/67376/1 "2022-12-08T09:44:26Z")

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Hello,  
I have a project Vision 8.1.16 with connection to PLC S71500.  
I can read all PLC variable but when try to write a PLC variable, I have this message:

Error writing to indice\_ciclo.value: Bad("Bad\_CommunicationError: A low level communication error occurred.")

What Can I do???

Thank you very much

Bye

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [December 8, 2022, 1:18pm UTC](https://forum.inductiveautomation.com/t/problem-writing-variable-to-plc-siemens-s7-1500/67376/2 "2022-12-08T13:18:31Z")

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Share more information. Is this an OPC connection, or are you using Ignition's Siemens driver? What address are you trying to write? What value are you trying to write? Does anything show up in the gateway log for these failures?

If using an OPC connection to Siemens' OPC server in the PLC, are you reading structures or single elements? If structures, are you writing the whole structure?

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<div class="post-metadata">

**Author:** ![stefano.sforna](https://avatars.discourse-cdn.com/v4/letter/s/91b2a8/32.png) [@stefano.sforna](https://forum.inductiveautomation.com/u/stefano.sforna)\
**Post date:** [December 8, 2022, 2:02pm UTC](https://forum.inductiveautomation.com/t/problem-writing-variable-to-plc-siemens-s7-1500/67376/3 "2022-12-08T14:02:00Z")

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I'm using a Ignition's Siemens driver S71500 to connect Ignition at Siemens CPU 1513.  
THis problem there is for all variables(integer, short, boolena etc...). Sometimes write operation is ok, sometimes no and there is this message:

Bad\_CommunicationError: A low level communication error occurred.

In the Device configuration of Ignition, PLC is connected  
I attached wrapper log

[wrapper.log](https://forum.inductiveautomation.com/uploads/short-url/fCnEXZmvHYWucQPCNYcUF2WqCPO.log) (310.5 KB)

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<div class="post-metadata">

**Author:** ![stefano.sforna](https://avatars.discourse-cdn.com/v4/letter/s/91b2a8/32.png) [@stefano.sforna](https://forum.inductiveautomation.com/u/stefano.sforna)\
**Post date:** [December 8, 2022, 3:30pm UTC](https://forum.inductiveautomation.com/t/problem-writing-variable-to-plc-siemens-s7-1500/67376/4 "2022-12-08T15:30:43Z")

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Is there a limit of Tag to connect at same device???  
I create a new device connected at the same Plc and I utilize this device only for 20 tags: I' don't have the problem.  
Can I create more device connected at same PLC Siemens to divide tags between different device????

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [December 8, 2022, 3:37pm UTC](https://forum.inductiveautomation.com/t/problem-writing-variable-to-plc-siemens-s7-1500/67376/5 "2022-12-08T15:37:21Z")

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There's no limit enforced in Ignition.

The logs you uploaded are full of errors happening during a write. It looks like you have some code that is trying to write a null value to a String tag multiple times per second.