# Modbus function 16 : Strange optimization

**URL:** <https://forum.inductiveautomation.com/t/modbus-function-16-strange-optimization/12070>\
**Category:** Ignition\
**Created:** [August 26, 2016, 9:02am UTC](https://forum.inductiveautomation.com/t/modbus-function-16-strange-optimization/12070 "2016-08-26T09:02:12Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Amarth](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/amarth/32/3313_2.png) [@Amarth](https://forum.inductiveautomation.com/u/Amarth)\
**Post date:** [August 26, 2016, 9:02am UTC](https://forum.inductiveautomation.com/t/modbus-function-16-strange-optimization/12070/1 "2016-08-26T09:02:12Z")

</div>

Hello all,

I’m trying to write data on a modbus salve device using the function 16.  
In order to do that, I created a modbus device and the addresses I require (basically 12 Holding Registers from address 1).  
In the designer, I created the 12 corresponding tags and a minimalistic script to write my data over these tags.

```auto
Tags = ["TagPath1", "TagPath2", ..., "TagPath12"]
Values = [value1, value2, ..., value12]

system.tag.writeAll (Tags, Values)
```

I expected the write command to be sent in an unique instruction but it appears that the items of the request have been optimized to 6 couples of items. (See following Capture)

[attachment=0]ASUR\_Function16.png[/attachment]

I had a look in the device advanced parameters but could not find any settings to change that.

My questions are:

[ul]  
[li]Is it the normal behavior ?[/li]  
[li]Is it possible to indicate to the driver that I want a unique request ? (Function 16 is already used but only for two items. I would like this function to be used for the twelve items)[/li][/ul]

Any advice ?

Thanks.

Ignition 7.8.3  
Java 1.8.91

---

<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 26, 2016, 3:06pm UTC](https://forum.inductiveautomation.com/t/modbus-function-16-strange-optimization/12070/2 "2016-08-26T15:06:23Z")

</div>

I think this might actually be fixed in 7.8.4. It looks like the ticket mistakenly didn’t get a release note associated with it.