S7 200 freeport setup

Hello guys,

I know another freeport question..

I am trying to set up communication between via a rs 232 digitizer to PLC. I am using hyper terminal at the mo to simulate the digitizer, as this is all quite new to me...

I managed to setup the majority of the program but the setup of the end of message for the received signal is driving me mad...

I need to be able to transmit to this card "xyz", let the card do its thing and then read the response. Presently I have have set this up BUT i have to tell the PLC via using an end character that the message is finished. I have tried to use the exceed time bit but no joy...

Could someone please help me

Regards

Matty

I have done some of this in the past, and I seem to remember also having issues with the exceed time setup.

Do you already know how long each response will be, or is it something that is varying?

Hello dwoodlock

I believe not long 100ms max, the message it self will consists of less then 10 chars, as basically makes up a weight in ACSII... I dont think I can even compare the message in the buffer as the value will always change...

Unless...

If i was to clear the receive buffer before I start a receive request I suppose I could always compare the value is great then 1, and would know that "something" is in the buffer??? What do you think?

I don't know if this document will help. From what I remember you need to create the code to 'index' increment through your memory location that you are writing data. If this is the case you will know how many bytes are read. If this is the case when you are done recieveing data (your incrementer is not longer incrementing) you will know how many bytes recieved and can move it to a new location, clear this buffer and reset your index.

Sorry if this was unclear... heading out of the office.



http://www.apostilastecnicas.com/Siemens/Siemens PLC Examples/TIP20.pdf

I kinda had something like this set up already... The bit I don't understand is how does the PLC know when the message has been sent, if it doesn't know that the message is in the first place??

Thank you again

Do you have a way of knowing how long the transmission time of the received message will be at its maximum?

If so perhaps you rcv instruction can be timed?

When I was working on this, I was trying to send evaluation information from a vision system to the S7-200. In this case, I left the recieve instruction active as long as I was'nt sending anything, I had a bit that was XIC for xmit and XIO for RCV.

I think this methodology got changed later on, because we had a set amount of bits that were being transferred every transmission back to the S7-200, so we knew that once we received bit 7 that the whole message had been sent.

Its hard to present a good solution for your application because you've not given us much information about it.