# Modbus 06 Write Function

**URL:** <https://forum.inductiveautomation.com/t/modbus-06-write-function/7874>\
**Category:** Ignition\
**Created:** [January 20, 2014, 4:01pm UTC](https://forum.inductiveautomation.com/t/modbus-06-write-function/7874 "2014-01-20T16:01:22Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![claudio](https://avatars.discourse-cdn.com/v4/letter/c/7cd45c/32.png) [@claudio](https://forum.inductiveautomation.com/u/claudio)\
**Post date:** [January 20, 2014, 4:01pm UTC](https://forum.inductiveautomation.com/t/modbus-06-write-function/7874/1 "2014-01-20T16:01:22Z")

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I need to write a value into a Modbus Register that is defined as Write Only using 06 function.  
Is there a way to define a Tag that writes into a register but doesn’t read from it?

If I define the tag as Read/Write it becomes in error, it returns null value and it doesn’t write into the destination register, I suppose because the register cannot be read.

Many thanks  
Claudio

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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:** [January 20, 2014, 4:35pm UTC](https://forum.inductiveautomation.com/t/modbus-06-write-function/7874/2 "2014-01-20T16:35:54Z")

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You can’t define a write-only tag, but you can write to the register from scripting using system.opc.writeValue().

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**Author:** ![illank86](https://avatars.discourse-cdn.com/v4/letter/i/c77e96/32.png) [@illank86](https://forum.inductiveautomation.com/u/illank86)\
**Post date:** [June 16, 2014, 3:52pm UTC](https://forum.inductiveautomation.com/t/modbus-06-write-function/7874/3 "2014-06-16T15:52:49Z")

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i have the same issue,

is there another solution to write to modbus register spesific bits, for example i want to write to register 157 bit 6, instead using script?

thanks 😃