Posted 12 Oct 2021 I am trying to create a simple `Hello World` Modbus TCP/IP program using Twincat3 and virtual PLC (PLC running locally on my computer). I have set up a LabVIEW Modbus TCP/IP master + slave program (both of which are working see screenshots below). I can send data between LabVIEW's master and slave programs. And also read the data from Python script (so I know for sure they are all working). Now I have tried to create a Twincat3 program to set some registers using Beckhoff example What I have tried: - I have tried changing the ipAddr parameter to: 'localhost', '192.168.88.1', '192.168.88.126' - Also I have tried the nUnitID set to: 0, 1, 16#FF (16#FF as specified by Beckhoff docs) This is my Beckhoff code: PROGRAM MAIN VAR ipAddr : STRING(15) := '192.168.88.1'; //Tried also 192.168.88.126 and 192.168.88.1 'localhost' M0 AT %MB0 : ARRAY [0..3] OF WORD; nValue : ARRAY [0..3] OF WORD; fbWriteRegs : FB_MBWriteRegs; bWriteRegs : BOOL; END_VAR IF NOT bWriteRegs THEN nValue[0] := nValue[0]+1; nValue[1] := nValue[1]+1; nValue[2] := nValue[2]+1; nValue[3] := nValue[3]+1; bWriteRegs := TRUE; fbWriteRegs.sIPAddr := ipAddr; fbWriteRegs.nTCPPort := 502; fbWriteRegs.nUnitID := 16#FF; //Tried setting this to 0,1 and it also and didnt work ... fbWriteRegs.nQuantity := 4; fbWriteRegs.nMBAddr := 16#3000; //Tried: 16#3000, 0, 1 fbWriteRegs.cbLength := SIZEOF(nValue); fbWriteRegs.pSrcAddr := ADR(nValue); fbWriteRegs.tTimeout := T#5S; fbWriteRegs (bExecute:=TRUE); ELSE IF NOT fbWriteRegs.bBUSY THEN bWriteRegs :=FALSE; fbWriteRegs (bExecute:=FALSE); END_IF fbWriteRegs (bExecute:=FALSE); END_IF What should I change in my code in order to make this example work? Thank you in advance for any support! Info about LabVIEW programs: I am using the Modbus TCP Master / Slave examples The IP address is set to localhost and the port to 502 (which should match the IP address in my Beckhoff code) I am 100% sure it works because I have also tried connecting to this program via Python script. Picture of my LabVIEW programs: Share this post Link to post Share on other sites