RS 232 for S7 300 Urgent!!!

hello all
i am new to ladder programming, i am using S7 300 PLC, i am unable to figure out how to send data to the plc (control commands) through rs232 cable i'll be glad if somebody can help me with this.
details: basically i have a program that should contol a process after receiving qeuries submmited by user from PC. i need to know how to send these queries (numbers or strings) to the plc and how the plc can read them. my plc is s7 300 from siemens it has one serial port only used for downloading the program

Hi there

You've got a long way to go on this.

The 9-pin port on the S7-300 is serial, but it uses RS485 electrically (not RS232) and it uses a Siemens' proprietary protocol, MPI.

To get something like unformatted ASCII characters or strings in to the PLC over RS232 you will require another module, a CP340 or CP341 comms card. There a number of standard function blocks for handling the data in the CP340 and CP341.

You want to know how to send these strings to the PLC? Well, it depends what you're sending them from. A PC? Another PLC? An IBM Blue Gene/L supercomputer?

You've not really given anything like enough under the heading 'details'. What you gave there is barely an overview. At the time I'm writing this 37 other people had viewed it without answer. You really need to flesh things out a bit.


Regards

Ken.

thanks ken

i have the s7300 plc giving output to drive circiuts of motors. these motors are supposed to move one head along three axes to bring an item. the user should request the item he wants thru LAN. requests can be taken from any pc in the lan to one server.

i was wondering if this server can then send the request thru serial port to the port in the plc.

regarding the cable i got from siemens an adapter that assures the data transfer from the RS232 to the RS485 (we use this to download the program to the plc from the pc.

i saw communication blocks in the step 7 version 5 but i don't know how to use them. can they be used to read info from the plc port without having to buy seperate module

thanks

X_GET and XPUT comm blocks work in MPI protocol or by its subset PPI protocol. You can read data from a Simens CPU S7-200 but you can't implement your protocol in the S7-300 using X_GET and X_PUT.
Best way, to make a protocol in your S7-300 as Ken M said, is the card CP340 and you'll control every single character.
Another way shold be implement a PPI protocol in your PC or buy a MPI driver for your PC.

hello all
this work is for university design project and we are building small prototype which, most probably, will be presented only one time. the university provide us with the plc with no extra module,
it is very important for us to do the job, but without buying new modules (which wont be used later on)
i would really appeciate it if you can provide me with more details about the PPI protocol and how it is done

thanks

PPI is Siemens proprietary protocol and Siemens gives (expensive) information to business partner only.

Try this links
PPI MPI info