[Visual-devel] Re: Dear Mr. Thomas Hergenhahn,

[Thomas H. <Tho...@we...>]

"Can Cui" <cac...@fh...> schrieb am 07.05.04 13:30:42: 
 
>Sorry to bother you again. 
No problem. 
> I would like to ask when we try to control the PLC via Internet, 
 
To prevent any misunderstanding: What is usually controlled via network are values 
inside the PLC. Controlling "the PLC" might also be understood as: Switch it to 
run/stop, load PLC program etc. That is NOT supported. 
 
(Ok, there are two extra programs, serialProxy and serialClient to "tunnel" serial 
connections over a network, but you need three computers and the original programming 
software, e.g. Step7 and you must shut down VISUAL while doing this). 
 
> how do we send operation commands from the client to the 
>server. The connection between client and server has already been set up. 
 
The client (HMI page) sends commands to the server, which will update values in the 
spreadsheet. You can watch the changes in the spreadsheet editor directly. 
 
On the other side, the server, if setup to do so, fetches data from the PLC(s) and 
writes back changes to the PLC(s). I think that shujat and arijit (excuse me if I 
mispelled their names)  are currently dealing with this part. 
 
Once this works, you can as well trigger updates by hand, inserting new values into a 
cell that is configured to be written to the PLC. 
 
So there is NO DIRECT operation that the client performs on the PLC. The idea of this 
concept is to make it most easy to: 
1) Test both parts without having the other yet ready 
2) Make it most easy to change PLC brand. 
 
HTH 
 
Thomas 
 
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