# SLC500 Communication Best Practices

**URL:** <https://forum.inductiveautomation.com/t/slc500-communication-best-practices/33285>\
**Category:** General Discussion\
**Created:** [March 20, 2020, 9:33pm UTC](https://forum.inductiveautomation.com/t/slc500-communication-best-practices/33285 "2020-03-20T21:33:53Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![mpstainbrook](https://avatars.discourse-cdn.com/v4/letter/m/aca169/32.png) [@mpstainbrook](https://forum.inductiveautomation.com/u/mpstainbrook)\
**Post date:** [March 20, 2020, 9:33pm UTC](https://forum.inductiveautomation.com/t/slc500-communication-best-practices/33285/1 "2020-03-20T21:33:53Z")

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Is there a SLC500 Communication Best Practices document available for connecting with Ignition Drivers?

Looking for something technical that explains the methods used to communicate with the CPU.

Limitations, capacities, impacts on Tag Group/Scan times?

Manual just explains how to make the connection.

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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:** [March 20, 2020, 9:38pm UTC](https://forum.inductiveautomation.com/t/slc500-communication-best-practices/33285/2 "2020-03-20T21:38:39Z")

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Best advice I've seen on here is from @pturmel:

> [@Typical Performance between Ignition and AB SLC 5/05](http://forum.inductiveautomation.com/t/typical-performance-between-ignition-and-ab-slc-5-05/17262/3):
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> Check “Comms Servicing Selection” and “MSG Servicing Selection” for channel 1 (S:2/15 & S:33/7). If either is set, it will crush your throughput, as only one request will be processed per scan (Comms) or per certain control flow instructions (MSG).

We don't have any guide. These things are old and slow, so only create tags for the data you need at as slow a rate as you can tolerate. Some people used leased scan classes to speed things up when tags are visible on a screen but disable or slow them down otherwise.

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**Author:** ![mpstainbrook](https://avatars.discourse-cdn.com/v4/letter/m/aca169/32.png) [@mpstainbrook](https://forum.inductiveautomation.com/u/mpstainbrook)\
**Post date:** [March 20, 2020, 10:26pm UTC](https://forum.inductiveautomation.com/t/slc500-communication-best-practices/33285/3 "2020-03-20T22:26:42Z")

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![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/2/2e709ec0129a8c8a3a8ef648928ae3862b006d57.png)

S:2/15 is certainly set. I changed to 0 and Connection Load Factors dropped. Will check Tag Response.

Thanks for this note.

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**Author:** ![Travis](https://avatars.discourse-cdn.com/v4/letter/t/bbce88/32.png) [@Travis](https://forum.inductiveautomation.com/u/Travis)\
**Post date:** [May 4, 2021, 3:30pm UTC](https://forum.inductiveautomation.com/t/slc500-communication-best-practices/33285/4 "2021-05-04T15:30:03Z")

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Thank you very much for this advice. After deselecting the Comms Servicing Sel S:2/15 bit, the load factor for this processor changed from 440% to 31%. Also, the fastest update we could get on these tags was about 30 seconds, and now it is 5 seconds as it should be. This helps a lot!  
Travis