# Synchronous write operation from Ignition thru PLC

**URL:** <https://forum.inductiveautomation.com/t/synchronous-write-operation-from-ignition-thru-plc/8674>\
**Category:** Ignition\
**Created:** [July 7, 2014, 12:43pm UTC](https://forum.inductiveautomation.com/t/synchronous-write-operation-from-ignition-thru-plc/8674 "2014-07-07T12:43:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![mazeyrat](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/mazeyrat/32/10955_2.png) [@mazeyrat](https://forum.inductiveautomation.com/u/mazeyrat)\
**Post date:** [July 7, 2014, 12:43pm UTC](https://forum.inductiveautomation.com/t/synchronous-write-operation-from-ignition-thru-plc/8674/1 "2014-07-07T12:43:38Z")

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I need to write data synchronously from Ignition thru PLC.  
A command has parameters, I need to be sure the PLC receive all the parameter before the command to trigger PLC operation.

When I use :  
system.tag.writeSynchronous  
or system.tag.writeAllSynchronous  
with an OPC SQlTags, is the write opeartion synchronous from Ignition , thru OPC-UA Server, thru PLC.  
(My OPC-Server is Kep, with Siemens S7 protocol) ???

When I use :  
system.opc.writeValue  
or system.opc.writeValues  
with opc item, is the write opeartion synchronous from Ignition , thru OPC-UA Server, thru PLC.  
(My OPC-Server is Kep, with Siemens S7 protocol) ???

When the Data are writtent by an opc client connected to Configurated Tag exposed by Ignition OPC-UA Server (7.7 feature), how to achieve synchronous write from this OPC client thru Ignition, thru Kep, to the PLC.  
If the client use synchronous write, it’s triggering a synchronous write in each layer ???

What is the best mean to obtain this kind of behaviors ![:scratch:](https://us1.discourse-cdn.com/inductiveautomation/original/1X/76d1620bec252bfac07050c889ff5a91dc8a9c25.gif ":scratch:")

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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:** [July 9, 2014, 6:36pm UTC](https://forum.inductiveautomation.com/t/synchronous-write-operation-from-ignition-thru-plc/8674/2 "2014-07-09T18:36:04Z")

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system.opc.writeValue is a synchronous call as much as it can be - what the server actually does with the write request is not controllable, but it’s probably safe to assume that it’s actually written the value when it returns the status for that service request.

system.tag.write is not synchronous, while system.tag.writeSynchronous is.

Writes to the exposed ‘configured tags’ are synchronous behind the scenes as well.

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<div class="post-metadata">

**Author:** ![mazeyrat](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/mazeyrat/32/10955_2.png) [@mazeyrat](https://forum.inductiveautomation.com/u/mazeyrat)\
**Post date:** [July 9, 2014, 6:56pm UTC](https://forum.inductiveautomation.com/t/synchronous-write-operation-from-ignition-thru-plc/8674/3 "2014-07-09T18:56:02Z")

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Thanks kevin,

When you say :  
Writes to the exposed ‘configured tags’ are synchronous behind the scenes as well,  
does it mean that if the ‘configured tag’ is an SQLTag OPC, the item is as well synchronously writed to the OPC-UA server ? or only the value in ignition Real Time DB ?

For system.tag.writeSynchronous for and SQLTag OPC, the item is synchronously writed to the OPC-UA server ? or only the value in ignition Real Time DB ?

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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:** [July 9, 2014, 7:07pm UTC](https://forum.inductiveautomation.com/t/synchronous-write-operation-from-ignition-thru-plc/8674/4 "2014-07-09T19:07:19Z")

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Both are synchronous to the OPC server.