# Problem writing Tag value for Bit in Siemens PLC via Ignition

**URL:** <https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925>\
**Category:** Ignition\
**Tags:** ignition79\
**Created:** [January 12, 2022, 2:01pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925 "2022-01-12T14:01:25Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Kartik\_I](https://avatars.discourse-cdn.com/v4/letter/k/8c91f0/32.png) [@Kartik\_I](https://forum.inductiveautomation.com/u/Kartik_I)\
**Post date:** [January 12, 2022, 2:01pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925/1 "2022-01-12T14:01:26Z")

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Hello All,

I am facing some issues while I am trying to write bit value for Siemens PLC. I am having a Word Datatype in which I need the second bit value should be written via Ignition but as I am writing the value it is going in the first bit of Word so anyone please suggest how to solve this issue.

Thanks,  
Kartik I

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**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:** [January 12, 2022, 2:15pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925/2 "2022-01-12T14:15:37Z")

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“some issues” is pretty vague. Please provide more information.

- Ignition version
- PLC model/version
- Whether using an OPC connection or an Ignition driver connection (and whether you followed the white paper instructions if the latter)
- Structure of your datatype and the element involved

{ I’m not a Siemens guy, but the ones around here will want to know. }

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<div class="post-metadata">

**Author:** ![Kartik\_I](https://avatars.discourse-cdn.com/v4/letter/k/8c91f0/32.png) [@Kartik\_I](https://forum.inductiveautomation.com/u/Kartik_I)\
**Post date:** [January 12, 2022, 2:44pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925/3 "2022-01-12T14:44:26Z")

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[quote=“pturmel, post:2, topic:54925”]

- Ignition version - Ignition 7.9
- PLC model/version - Siemens 1500 PLC
- Whether using an OPC connection or an Ignition driver connection (and whether you followed the white paper instructions if the latter) - **Siemens 1500 Driver**
- Structure of your datatype and the element involved - **Dword Structure**

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**Author:** ![zxcslo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zxcslo/32/61610_2.png) [@zxcslo](https://forum.inductiveautomation.com/u/zxcslo)\
**Post date:** [January 12, 2022, 2:49pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925/4 "2022-01-12T14:49:18Z")

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**Set bit:**

```auto
new_tag_value = old_tag_value | (1<<bit_number)

```

**Clear bit:**

```auto
new_tag_value = old_tag_value & ~(1<<bit_number)

```

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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:** [January 12, 2022, 3:05pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925/5 "2022-01-12T15:05:29Z")

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In case zxcslo’s brief reply confuses you, it means there isn’t support in the PUT/GET protocol to change just one bit of a word or dword. You have to write the whole value. (Which can conflict with PLC logic writing to other bits–so don’t if that would apply.)

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<div class="post-metadata">

**Author:** ![Kartik\_I](https://avatars.discourse-cdn.com/v4/letter/k/8c91f0/32.png) [@Kartik\_I](https://forum.inductiveautomation.com/u/Kartik_I)\
**Post date:** [January 12, 2022, 3:12pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925/6 "2022-01-12T15:12:11Z")

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Thanks I will check.

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<div class="post-metadata">

**Author:** ![Kartik\_I](https://avatars.discourse-cdn.com/v4/letter/k/8c91f0/32.png) [@Kartik\_I](https://forum.inductiveautomation.com/u/Kartik_I)\
**Post date:** [January 12, 2022, 3:52pm UTC](https://forum.inductiveautomation.com/t/problem-writing-tag-value-for-bit-in-siemens-plc-via-ignition/54925/7 "2022-01-12T15:52:41Z")

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I used the XOR function with Left Shift Bit so its good now. **But I have a another doubt regarding WString Datatype how to fetch this String Datatype in ignition.**