# Polling OPC event base

**URL:** <https://forum.inductiveautomation.com/t/polling-opc-event-base/4942>\
**Category:** General Discussion\
**Created:** [August 7, 2012, 11:13am UTC](https://forum.inductiveautomation.com/t/polling-opc-event-base/4942 "2012-08-07T11:13:54Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![daneshy](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@daneshy](https://forum.inductiveautomation.com/u/daneshy)\
**Post date:** [August 7, 2012, 11:13am UTC](https://forum.inductiveautomation.com/t/polling-opc-event-base/4942/1 "2012-08-07T11:13:54Z")

</div>

Dear experts,

I have a problem, I need read modbus data with ignition OPC only when a flag set to 1, means when the flag set to 0 I want to not reading data with OPC.  
Is it possible?

Regards,  
Mohammad Javad

---

<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 7, 2012, 2:52pm UTC](https://forum.inductiveautomation.com/t/polling-opc-event-base/4942/2 "2012-08-07T14:52:17Z")

</div>

You can use “driven” scan classes for this. See [here](http://inductiveautomation.com/support/usermanuals/ignition/scan_classes.htm?zoom_highlightsub=driven%2Bscan) in the user manual.

---

<div class="post-metadata">

**Author:** ![Colby.Clegg](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/colby.clegg/32/3282_2.png) [@Colby.Clegg](https://forum.inductiveautomation.com/u/Colby.Clegg)\
**Post date:** [August 8, 2012, 6:46pm UTC](https://forum.inductiveautomation.com/t/polling-opc-event-base/4942/3 "2012-08-08T18:46:31Z")

</div>

And in addition to the driven mode, change “OPC Data Mode” to “Read” instead of “Subscribe”.

Regards,