TwinCAT local AmsNetId can be changed using Router->Change AmsNetId from tray icon menu.

But what if you want to change the AmsNetId manually from your own program or script? Obviously the tray menu does something under the hood.

Current AmsNetId location

I already knew that the Windows registery has the AmsNetId as a value under Computer\HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Beckhoff\TwinCAT3\System. The address is as a hexadecimal binary, like in the following figure c0 a8 05 83 01 01 is 192.168.5.131.1.1.

I first tried to change it directly editing it in regedit but it just didn’t work out.

Finding how it is done

As the current address is in the registery, I assumed that the tray icon does something to registery too.

I used a great tool RegistryChangesView by Nir Sofer from https://www.nirsoft.net/utils/registry_changes_view.html - it lists all registery changes that have occured during two snapshots.

By first taking a snapshot of registery with old AmsNetId and then again after changing it to 192.168.5.131.1.2 for testing, we can see clearly what happens:

A new registery value with name RequestedAmsNetId was added to HKEY_LOCAL_MACHINE\Software\WOW6432Node\Beckhoff\TwinCAT3\System. So the way to change AmsNetId is not to edit existing one - instead a new temporary value needs to be added!

Solution

Using .reg file

Using simple .reg file the AmsNetId can be changed. So create a file like change.reg with contents similar to the following (just change the values the one you like).

Note that a reboot is required to really change it.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\Software\WOW6432Node\Beckhoff\TwinCAT3\System]
"RequestedAmsNetId"=hex(3):C0,A8,05,83,01,02

Using C#

A simple code using C# under .NET Framework can also do the trick. Note that the application needs to be run as an administrator.

//Using Microsoft.Win32
var key = Registry.LocalMachine.OpenSubKey(@"Software\WOW6432Node\Beckhoff\TwinCAT3\System", true);
key.SetValue("RequestedAmsNetId", new byte[] { 192, 168, 5, 131, 1, 2 }, RegistryValueKind.Binary);