# Maximum Number of Modbus Registers

**URL:** <https://forum.inductiveautomation.com/t/maximum-number-of-modbus-registers/91262>\
**Category:** Ignition\
**Tags:** ignition80, ignition81\
**Created:** [June 3, 2024, 6:23am UTC](https://forum.inductiveautomation.com/t/maximum-number-of-modbus-registers/91262 "2024-06-03T06:23:35Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Santhosh\_Pugalenthi](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Santhosh\_Pugalenthi](https://forum.inductiveautomation.com/u/Santhosh_Pugalenthi)\
**Post date:** [June 3, 2024, 6:23am UTC](https://forum.inductiveautomation.com/t/maximum-number-of-modbus-registers/91262/1 "2024-06-03T06:23:35Z")

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When I try to create around 700 Modbus Registers in Ignition Gateway, I got internal error when I click on save button.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/5/d5a8b45b776c487f1ab51cd7846806d48fb97767.png)  
and I got "Form is larger than max length 200000" in Gateway Logs  
 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/e/7/e73feb3c598e90aeb9fad73d1fb6342e0162fd45.png)  
Can anyone please explain the maximum number of registers that we can add to a Modbus TCP Device in ignition 8.1.13?

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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:** [June 3, 2024, 11:52am UTC](https://forum.inductiveautomation.com/t/maximum-number-of-modbus-registers/91262/2 "2024-06-03T11:52:59Z")

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The limit is due to use of the address map. Don't use the address map, and you won't have any limit.

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**Author:** ![Cody\_Morgan](https://avatars.discourse-cdn.com/v4/letter/c/db5fbb/32.png) [@Cody\_Morgan](https://forum.inductiveautomation.com/u/Cody_Morgan)\
**Post date:** [June 4, 2024, 3:52pm UTC](https://forum.inductiveautomation.com/t/maximum-number-of-modbus-registers/91262/3 "2024-06-04T15:52:05Z")

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Hi @Santhosh_Pugalenthi!

@pturmel is correct, 700 rows is too large for the address mapping feature in the gateway. Are you treating each row as a separate register or tag? If so, you are probably much better off manually creating the tags. Here's the relevant page in our documentation: [Modbus - Manually Addressing](https://docs.inductiveautomation.com/docs/8.1/ignition-modules/opc-ua/opc-ua-drivers/modbus#manually-addressing)

Alternatively, you can try grouping your tags so that each row in the address map represents more than one tag. I believe the form limitation is based only on the number of rows, not tags or registers.

Personally, I believe tags that are manually addressed are easier to understand. I would recommend that approach.

If you can share more about what you are trying to do, I would be happy to provide more specific examples.

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**Author:** ![earnhartj84](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/earnhartj84/32/29405_2.png) [@earnhartj84](https://forum.inductiveautomation.com/u/earnhartj84)\
**Post date:** [June 4, 2024, 4:00pm UTC](https://forum.inductiveautomation.com/t/maximum-number-of-modbus-registers/91262/4 "2024-06-04T16:00:25Z")

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Here are some examples of direct Modbus mapping.  
ns=1;s=[Test\_Bench\_Micro]C6 (coil) (Bool)  
ns=1;s=[Test\_Bench\_Micro]HR10 (Integer)  
ns=1;s=[Test\_Bench\_Micro]HRF3 (Real)(Float)

Type this directly into the Tag Browser

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/3/c/3ce7d689f14a6b3418424e91ea445dfbff746f25.png)