# Modbus basic connection to simulator

**URL:** <https://forum.universal-robots.com/t/modbus-basic-connection-to-simulator/35259>\
**Category:** Robot Communication\
**Created:** [July 15, 2024, 8:41pm UTC](https://forum.universal-robots.com/t/modbus-basic-connection-to-simulator/35259 "2024-07-15T20:41:15Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![abalalimoghaddam](https://avatars.discourse-cdn.com/v4/letter/a/e9a140/32.png) [@abalalimoghaddam](https://forum.universal-robots.com/u/abalalimoghaddam)\
**Post date:** [July 15, 2024, 8:41pm UTC](https://forum.universal-robots.com/t/modbus-basic-connection-to-simulator/35259/1 "2024-07-15T20:41:15Z")

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Hi All,  
I am trying to test the Modbus communication with our UR10 in a bare minimum setup first but I have not been able to yes. Here is what I have tried so far:

- Connected the robot and a pc to the same switch
- Run open mod sim on the PC and connect it. I open the coil status window which by default shows all coils are set to 0
- I turn off firewall and use another computer to make sure I can ping the PC
- On UR teach pendant I add a new modbus unit with IP of the PC
- I add a digital output signal to this unit
- I create a simple program which sets that digital output to High
- I run the program expecting to see the value at coil 00001 to change from 0 to 1 but I see no change
- After about a minute I see the following error message (please see screenshot attached) which refers to code 0 but I am unable to find what code 0 means

Could anyone help me troubleshoot this or give me suggestions on how to create a minimal Modbus setup to test?

Thank you!

 ![PXL_20240715_200154863.MP](https://us1.discourse-cdn.com/flex020/uploads/universal_robots/original/2X/c/ce8a767f377d9529436a3dc370f345c484d68264.jpeg)  
 ![PXL_20240715_202210210.MP](https://us1.discourse-cdn.com/flex020/uploads/universal_robots/original/2X/6/60399999dc21f54fbe93c98d91c39bcbfa0dcabb.jpeg)