# Modbus Addresses over 65535

**URL:** <https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438>\
**Category:** Ignition\
**Tags:** ignition81\
**Created:** [August 28, 2023, 6:57am UTC](https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438 "2023-08-28T06:57:09Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Laurence\_Brewer](https://avatars.discourse-cdn.com/v4/letter/l/919ad9/32.png) [@Laurence\_Brewer](https://forum.inductiveautomation.com/u/Laurence_Brewer)\
**Post date:** [August 28, 2023, 6:57am UTC](https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438/1 "2023-08-28T06:57:09Z")

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Hello I have an application where I need to address modbus registers in the 400 000 to 449 651, but when creating address rows in my modbus device on the gateway, the register address is limited to 65 535. Is there a way to address modus registers over 65 536?

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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:** [August 28, 2023, 7:11am UTC](https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438/2 "2023-08-28T07:11:17Z")

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Are you sure the address syntax you’re being fed isn’t using the leading 4 to indicate it’s a Holding Register, and the addresses are in the 0 to 49651 range?

Anything above 65535 isn’t Modbus because it isn’t a 2 byte address any more.

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<div class="post-metadata">

**Author:** ![Laurence\_Brewer](https://avatars.discourse-cdn.com/v4/letter/l/919ad9/32.png) [@Laurence\_Brewer](https://forum.inductiveautomation.com/u/Laurence_Brewer)\
**Post date:** [August 28, 2023, 7:18am UTC](https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438/3 "2023-08-28T07:18:17Z")

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These are the register addresses, the only thing I can think is that heaxadecimal addressing would allow for high register addresses.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/6/c/6c003ea9112ad66c86e7c58f85b1ea5b9e105c8f.png)

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<div class="post-metadata">

**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:** [August 28, 2023, 7:21am UTC](https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438/4 "2023-08-28T07:21:57Z")

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Ignore the leading 4 and hope for the best.

Don’t use the address map until you’ve verified any addresses work. Create OPC tags manually, using the modbus addressing syntax described in the manual. Try unit/slave id 1 if the default 0 doesn’t work.

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<div class="post-metadata">

**Author:** ![Laurence\_Brewer](https://avatars.discourse-cdn.com/v4/letter/l/919ad9/32.png) [@Laurence\_Brewer](https://forum.inductiveautomation.com/u/Laurence_Brewer)\
**Post date:** [August 28, 2023, 7:25am UTC](https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438/5 "2023-08-28T07:25:15Z")

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Thanks,

I think that it is a good chance that the addresses have got a prefix of 4 tacked on.

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<div class="post-metadata">

**Author:** ![carles.centeno](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/carles.centeno/32/67402_2.png) [@carles.centeno](https://forum.inductiveautomation.com/u/carles.centeno)\
**Post date:** [August 31, 2023, 5:50pm UTC](https://forum.inductiveautomation.com/t/modbus-addresses-over-65535/78438/6 "2023-08-31T17:50:26Z")

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Number 4 meaning that this register is a Holding Register (2 bytes). 0-65535  
400123 is holding register register 123.