You will need to know the Modbus registers in the SCADAPack that you need to write to. Then use function code 6 to write to a single register or 16 for multiple registers. Or you can have the SCADAPack read the info from your PLC. So if you are not programming the SCADAPack I would get with the programmer of it and talk about the best way to do this. It may end up simpler than you think.