# Modbus RTU to Compactlogix write function code 5

**URL:** <https://forums.digi.com/t/modbus-rtu-to-compactlogix-write-function-code-5/7480>\
**Category:** Digi One IA/IAP\
**Created:** [April 16, 2009, 11:55pm UTC](https://forums.digi.com/t/modbus-rtu-to-compactlogix-write-function-code-5/7480 "2009-04-16T23:55:58Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![fnor](https://avatars.discourse-cdn.com/v4/letter/f/49beb7/32.png) [@fnor](https://forums.digi.com/u/fnor)\
**Post date:** [April 16, 2009, 11:55pm UTC](https://forums.digi.com/t/modbus-rtu-to-compactlogix-write-function-code-5/7480/1 "2009-04-16T23:55:58Z")

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I have a arcon polling my Compactlogix L32e via modbus RTU to enthernet/IP  
I (or the person writing to me gets a "illegal function code was sent to unit.  
How do I get past this?  
The modbus address is 900 901 and 902.  
I have mapped accoeding to 90000653-b  
help