# Modbus TCP connection problem **URL:** \ **Category:** Ignition\ **Created:** [November 9, 2017, 4:23am UTC](https://forum.inductiveautomation.com/t/modbus-tcp-connection-problem/15940 "2017-11-09T04:23:50Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Rthan](https://avatars.discourse-cdn.com/v4/letter/r/d2c977/32.png) [@Rthan](https://forum.inductiveautomation.com/u/Rthan)\ **Post date:** [November 9, 2017, 4:23am UTC](https://forum.inductiveautomation.com/t/modbus-tcp-connection-problem/15940/1 "2017-11-09T04:23:50Z")
Hi everyone, Probably this is the topic that has already been discussed. I am using Ignition version 7.9.4 to connect to Panasonic FP0H PLCs using Modbus TCP. I am still in the initial stage of device connection. However, the connection status keeps changing from connected to disconnected time to time, and I’m worried if this continues, I might have bad tagging problems. I have searched and tried what other people has mentioned in these forums but they don’t work. I have tried increasing the communication timeout from “2000” up to “30000” but the problem still remains. I also have tried decreasing max holding registers and max input registers to save the scan time but doesn’t work. ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/d/d4fa897cb656e7b8528a8cee4e1e945ba927a318.png) I have attached the communication settings for my PLC (hopefully it can be viewed) I have changed the TCP ULP timeout time to 20\*100ms to match my Ignition setting but the problem persists. Appreciate any help from you guys. Thanks. ---
**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:** [November 9, 2017, 12:46pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-connection-problem/15940/2 "2017-11-09T12:46:08Z")
If you haven’t subscribed to any tags yet this is common with Modbus devices. ---
**Author:** ![Rthan](https://avatars.discourse-cdn.com/v4/letter/r/d2c977/32.png) [@Rthan](https://forum.inductiveautomation.com/u/Rthan)\ **Post date:** [November 10, 2017, 4:24am UTC](https://forum.inductiveautomation.com/t/modbus-tcp-connection-problem/15940/3 "2017-11-10T04:24:42Z")
Thank you for your reply. I also have a problem with subscribing the tags, as I am getting null values all along. I used holding register 40001-40006 in my PLC, and retrieve the value from Ignition with " [Modbus]HR1 ". Since my stored value in the register is “unsigned integer”, I also tried " [Modbus]HRUS1 " but they both do not work. I have attached part of my error log since the log file I have is too big to attach. Hope you could help. Thanks. ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/8/8ba9c9d6b87c7afcd3facf756d4eaf9fb1dd80ef.png) ---
**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\ **Post date:** [November 10, 2017, 4:15pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-connection-problem/15940/4 "2017-11-10T16:15:29Z")
You may need to specify a particular unit ID (may be listed as a ‘slave ID’ or something similar in your device configuration). This can be pre-pended to the register path, ie: `[Modbus]2.HR1` or similar. ---
**Author:** ![dturner](https://avatars.discourse-cdn.com/v4/letter/d/90ced4/32.png) [@dturner](https://forum.inductiveautomation.com/u/dturner)\ **Post date:** [November 13, 2017, 9:58pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-connection-problem/15940/5 "2017-11-13T21:58:22Z")
How many connections your Panasonic FP0H support? Is Ignition the only thing that is connecting to the PLC?