This is how I write Modbus Master (* DCOMCONTROL MANAGEMENT *) LDR %M1 [ %MW0:12 := 0 ] [ %MW0 := 16#010C ] [ %MW1 := 16#0007 ] [ %MW2 := 16#0510 ] (*10 is my modbus code*) [ %MW3 := 1234 ] (*Address of the word to write*) [ %MW4 := 16#0002 ] (*N = Number of words to write*) [ %MW5 := 16#0004 ] (*00, 2*N*) [ %MW6 := 16#000F ] I hope this helped you.