Siemens SIMATIC NET CP 243-1, Руководство по эксплуатации

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Application and properties
1.6 IT communication
CP 243-1
Operating Instructions, 03/2012, C79000-G8976-C244-02
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Performance/constraints
FTP communication is subordinate to S7 communication. This means that the reaction times
of FTP communication depend on the particular configuration and cannot be predicted in
general terms.
Note
Only one FTP client can access the FTP server at any one time. When the FTP server of the
CP 243-1 is accessed by the S7 user program via the FTP client function, access by a
remote FTP client is not possible. The reverse also applies.
1.6.5 FTP client
How it works
The FTP client of the CP 243-1 can be used to transfer data from an S7-200 system to the
file system of an FTP server, or the contents of a file can be copied to the DB of the local S7-
200 system.
You can choose whether to transfer a file completely or only part of it. The number of bytes
to be transferred can be specified for a read or write request.
If 0 is specified as the number of bytes to be transferred in a write request, an empty file with
the name specified in the write request is created in the file system of the addressed FTP
server. The length 0 in a read request means that the specified file is transferred completely
to the DB of the local S7-200 system assuming that this does not exceed its storage space.
If the number of bytes to be read is specified for a read request, this must match the length
of the file to be read. Otherwise the CP 243-1 reports an error when the read request is
executed.
The FTP client can also be used to delete specified files in the file system of an FTP server
initiated by the local S7-200 system.
When transferring files with FTP, the files being replaced are not modified and the data they
contain is not converted. All the data to be transferred is taken as bytes. The data to be
written is stored as bytes in the specified file.
The FTP client of the CP 243-1 always initiates the file transfer, triggered by the S7-200 user
program. An FTP server itself does not generate FTP requests.
The CP 243-1 only accepts one FTP client request at a time from the S7-200 user program.
As soon as this is completely processed, the CP 243-1 returns a positive or negative
acknowledgment. Only then can the S7-200 user program send a new FTP client request.