Serial interface between S7 300 and LabView

[Hprosjplc]

Hi! Right now we are woring on our main project wich consist partly of connecting two Siemens S7-300 PLC`s together with modbus /TCP/IP, and having a labView control and monitoring station at each end. Please, don`t ask why, it`s a challenging task Now.. My problem at this moment is making labview talk to one of the PLC`s trough a CP340 serial module, and nullmodem cable. I have already downloaded the manual, and used it in detail as a guide. When i use terminal to send a hex character to the PLC i get an answer, wich always is "15". My question is what software i need to enterpet these hex og ascii transmissions so labview chan send and recieve information to and form the plc. To be accurate, this is an S7 300 CPU314 IFM (314-5AE01-0AB0). And, are there any guides as to how to get the CP340 module to sendt selectet parts of info to PC(labview)? Thank you very much for all help.

[Hprosjplc]

Anyone? I have gone trough all the blocks that comes stock with the CP340, and still i can´t figure out how to establish communication. When i flick a switch in Labview, i want to activate an output on the PLC and vica-versa. Do i need an OPC server? Or some sort of USB/PCMCIA/ETHERNET card in between, or just use a direct serial connection?

[Rod_Hackney]

It is my understanding that you are connecting together a S7-300 with a PC running labview. It sounds like you have a serial interface box you are trying to connect. The standard S7-300 series has a 9 pin serial port on it. Its protocol is MPI. You will need to make sure your serial interface supports MPI. Also, the labview will have to have a Siemens MPI serial communication driver running to allow you to read/write to the plc. I would check the with national instruments about labview communication drivers and siemens about interface to the specific S7-300 series processor you have.