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Thanks esload. I have tried that and my controller still cannot talk/control the slave over modbus. I need to change bit 0 to a value of one in register number 705 of a modbus slave. what would be the values of %MW3, %MW5, %MW6 and %MW7 in my control table? I thank you for your help.

Hi, I need to connect a Twido to a TeSys U motor starter. The starter has a modbus module that can be used for remote comms. I understand that I need to use EXCH instruction but I am not very clear on how it is used and needs to be setup in twidosoft. I wold appreciate some help on this matter. This is how I have tried to implement it but it doesnt seem to work: (* RESET DATA EXCHANGE *) BLK %MSG2 LD %I0.0.1 R END_BLK (* INITIALIZE CONTROL TABLE *) LDR %I0.0.2 [ %MW0:15 := 0 ] [ %MW0 := 16#010C ] (* transmission length *) [ %MW1 := 16#0007 ] (* transmission reception offset *) [ %MW2 := 16#0503 ] (* address/ request code.. 05 is address, 03 is modbus code *) [ %MW3 := 455 ] (*control word... register of starter that has the info*) [ %MW4 := 2 ] (* no.of words to write*) (* 0 = REQUEST ACTIVE; 1 = READY TO TRANSMIT *) LDR %I0.0.2 [ %MW6 := 16#0000 ] (* high word data *) [ %MW7 := 16#000F ] (* low word data *) AND %MSG2.D [ EXCH2 %MW0:12 ] This is adapted from another application I found that uses EXCH2 instruction. I would appeciate if someone could help me out here, specifically on calculating the transmission length, offsets and word data etc. Thank you.