Modbus tcp server/slave unable to use slaveID other than default

[smk422]

start a modbus tcp server listening with a slaveID = 1, 2, 3 or other. According to Copilot, this is a bug.

Exception has occurred: CLR/System.Collections.Generic.KeyNotFoundException
An unhandled exception of type 'System.Collections.Generic.KeyNotFoundException' occurred in System.Private.CoreLib.dll: 'No unit found for the specified unit identifier.'
at FluentModbus.ModbusServer.Find(Byte unitIdentifier, Dictionary2 map) at FluentModbus.ModbusServer.GetHoldingRegisterBuffer(Byte unitIdentifier) at FluentModbus.ModbusServer.GetHoldingRegisterBuffer[T](Byte unitIdentifier) at ScadaPlus.Integration.Modbus.ModbusSlave.EnsureUnitInitialized(Byte unitId) in c:\develop\sp-edge-integration-server\ScadaPlus.Integration.Modbus\ModbusSlave.cs:line 74 at ScadaPlus.Integration.Modbus.ModbusSlave.startServer() in c:\develop\sp-edge-integration-server\ScadaPlus.Integration.Modbus\ModbusSlave.cs:line 48 at ScadaPlus.Integration.Modbus.Slave.Collector.<ExecuteAsync>d__7.MoveNext() in c:\develop\sp-edge-integration-server\Scada.Integration.Modbus.Slave\Collector.cs:line 57 at Microsoft.Extensions.Hosting.Internal.Host.<<StartAsync>b__15_1>d.MoveNext() at Microsoft.Extensions.Hosting.Internal.Host.<ForeachService>d__181.MoveNext()
at Microsoft.Extensions.Hosting.Internal.Host.d__15.MoveNext()
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.d__4.MoveNext()
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.d__4.MoveNext()
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(IHost host)
at ScadaPlus.Integration.Modbus.Slave.Program.Main(String[] args) in c:\develop\sp-edge-integration-server\Scada.Integration.Modbus.Slave\Program.cs:line 16

[jindongjie]

Same situation.Hope for fix.

[jindongjie]

Hi, i think i solved the problem after anlyzing the code and practicing on my project.
The fix should be call public void AddUnit(byte unitIdentifer) function to add a new unitIdentifer (in RTU term slaveID) before we use that slaveID to connect with server. It is both avaliable for "ModbusTCPServer" and "ModbusRTUServer" because they both inherit from "ModbusServer" class.

[jindongjie]

I strongly recommend adding clear notifications in the documentation and exception error hints. I switch from NModbus to this project for its advanced register handling, and users shouldn’t be blocked by such simple setup issues.

[jindongjie]

Also don't forget use public Span<short> GetHoldingRegisters(byte unitIdentifier = 0) function to get holdingregisters or any other registers. So you able to modify the correct Registers instead of default unitIdentifier = 0.