# 8.3 Modbus TCP connection - difference from 8.1? **URL:** \ **Category:** Ignition\ **Tags:** ignition83\ **Created:** [January 6, 2026, 5:37pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102 "2026-01-06T17:37:48Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![tgarrison](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/tgarrison/32/80965_2.png) [@tgarrison](https://forum.inductiveautomation.com/u/tgarrison)\ **Post date:** [January 6, 2026, 5:37pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/1 "2026-01-06T17:37:48Z")
I'm migrating a server from 8.1.50 to 8.3.2. All the devices connected are Modbus TCP connections (modicons). It's an inherited mess that I'm trying to straighten out a touch. There are a number of OPC tags that refer to modbus addresses that don't have a mapping in the PLC. Mostly bools. In 8.1, those tags seem to semi-randomly be set to either T or F. In 8.3, those same tags are returning an "Error" status, [null, Error("CreateMonitoredItems failed: Bad\_NodeIdUnknown: The node id refers to a node that does not exist in the server address space."), Tue Jan 06 10:26:39 CST 2026 (1767716799767)] Is that an expected difference in how 8.3 is handling such items? Or did I miss a setting somewhere? I prefer the Error, as it's more definitive for me as to which devices ACTUALLY have which tags. ---
**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:** [January 6, 2026, 5:58pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/2 "2026-01-06T17:58:39Z")
Nothing changed, Bad\_NodeIdUnknown with the Modbus driver probably means a bad/invalid address, which means either the address mapping isn't right, or the OPC Item Path isn't right. If it's the OPC Item Path the likely cause would be something to do with UDT params resolving or not resolving... look at these tags and see what's going on. ---
**Author:** ![tgarrison](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/tgarrison/32/80965_2.png) [@tgarrison](https://forum.inductiveautomation.com/u/tgarrison)\ **Post date:** [January 6, 2026, 6:05pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/3 "2026-01-06T18:05:11Z")
Same tags. Looking at the tag diagnostics, there is a slight difference, and I'm guessing it's from the Ignition OPC-UA server. I know the modbus address is not mapped in the PLC, so that "false" that is getting returned on 8.1.50 isn't "real" 8.1.50: Last Published Value: [false, Error\_Configuration("Bad\_NodeIdUnknown: The node id refers to a node that does not exist in the server address space."), Mon Nov 10 09:24:49 CST 2025 (1762788289759)] 8.3.2: Last Published Value: [null, Error("CreateMonitoredItems failed: Bad\_NodeIdUnknown: The node id refers to a node that does not exist in the server address space."), Tue Jan 06 10:26:39 CST 2026 (1767716799767)] ---
**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:** [January 6, 2026, 6:06pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/4 "2026-01-06T18:06:25Z")
Those are effectively the same error, so whatever your problem is it's happening in 8.1 and 8.3. ---
**Author:** ![tgarrison](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/tgarrison/32/80965_2.png) [@tgarrison](https://forum.inductiveautomation.com/u/tgarrison)\ **Post date:** [January 6, 2026, 6:07pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/5 "2026-01-06T18:07:34Z")
They're the same underlying error, but the tag browser in 8.1.50 shows the tag as being perfectly fine, with a False value. In 8.3.2, it shows as "Error". And bindings react differently. ---
**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:** [January 6, 2026, 6:08pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/6 "2026-01-06T18:08:43Z")
I think what you might be seeing is that we fixed the fact that checkboxes in the Tag Browser didn't indicate bad quality in any meaningful way. Your tags were never "perfectly fine" when they had bad quality. Not sure about your bindings problem, maybe talk to support and explain the difference. ---
**Author:** ![tgarrison](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/tgarrison/32/80965_2.png) [@tgarrison](https://forum.inductiveautomation.com/u/tgarrison)\ **Post date:** [January 6, 2026, 6:11pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/7 "2026-01-06T18:11:04Z")
Gotcha. I'm glad you made the fix. As it's much easier having that bad quality be visible.. ---
**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:** [January 6, 2026, 6:14pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/8 "2026-01-06T18:14:34Z")
Can you provide some screenshots of the difference you're seeing in the Tag Browser? I'm starting to wonder if the improvement to uncertain/bad quality for booleans was actually implemented or just planned... in which case I don't know what you're seeing. ---
**Author:** ![tgarrison](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/tgarrison/32/80965_2.png) [@tgarrison](https://forum.inductiveautomation.com/u/tgarrison)\ **Post date:** [January 6, 2026, 6:17pm UTC](https://forum.inductiveautomation.com/t/8-3-modbus-tcp-connection-difference-from-8-1/113102/9 "2026-01-06T18:17:26Z")
Definitely appears to be implemented. 8.1: ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/b/1/b1aad082687966038b22bedfeffe1017875cf3e6.png) 8.3: ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/4/4/446313b7975a3a5c49e496d1011e560c59e9b580.png)