# Modbus server, error reading data

**URL:** <https://forum.universal-robots.com/t/modbus-server-error-reading-data/31147>\
**Category:** Robot Communication\
**Created:** [October 29, 2023, 12:55pm UTC](https://forum.universal-robots.com/t/modbus-server-error-reading-data/31147 "2023-10-29T12:55:05Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![risto.ojala](https://avatars.discourse-cdn.com/v4/letter/r/b2d939/32.png) [@risto.ojala](https://forum.universal-robots.com/u/risto.ojala)\
**Post date:** [October 29, 2023, 12:55pm UTC](https://forum.universal-robots.com/t/modbus-server-error-reading-data/31147/1 "2023-10-29T12:55:06Z")

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Hey, I’m trying to read data from the Modbus TCP server of a UR5E robot (polyscope version 5.13.1). I’m following this video tutorial: [https://www.youtube.com/watch?v=Pw7FKbPZkIk](https://www.youtube.com/watch?v=Pw7FKbPZkIk)

The robot controller is connected to my PC via ethernet, and both devices have static IP addresses in the same subnet. Connection is succesfully established between the controller and my PC. However, I get the below error when trying to read data from the modbus server registers:

![qmodmaster](https://us1.discourse-cdn.com/flex020/uploads/universal_robots/original/2X/5/51e66cae083142004b4357c8efda2bf1e6c6daca.png)

The server registers are readable from the robot controller itself via URScript. However, externally I cannot access the values.

Any help would be much appreciated!

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<div class="post-metadata">

**Author:** ![WattsUp](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.universal-robots.com/wattsup/32/5732_2.png) [@WattsUp](https://forum.universal-robots.com/u/WattsUp)\
**Post date:** [October 30, 2023, 3:01pm UTC](https://forum.universal-robots.com/t/modbus-server-error-reading-data/31147/2 "2023-10-30T15:01:19Z")

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Try setting Unit ID to 0, and I always start by reading start address 256 to pull controller version number.

Also note, some Modbus systems start address at 0, some start at 1. Depending on that your reads/writes can be off by one.

![image](https://us1.discourse-cdn.com/flex020/uploads/universal_robots/original/2X/6/6eef7ac0c2d5bf9a21c57547a5efdac77f3b97f6.png)