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3 Interface Modules
3.2.4 Possible communication links within the framework of the ISO 7-layer model
The more implemented layers are replaced by user-specific definitions
the more provisions the user has to make for proper message frame
The following diagram shows a possible application for variable configuring of message frames:
CNC
An external device uses the imaginary procedure XYZ. This procedure waits for the 20H
control character to be transmitted; it acknowledges reception of this character with the 40H
character.
When using this procedure for data transfer, the user must therefore proceed as follows:
1) The user sends a message frame with only one usable data - namely, 20H - which is
neither embedded in the SINUMERIK 850/880 message frame specification nor in the
AS 512 protocol. For this purpose, the user selects the TRANSPARENT procedure to be
able to transfer this data in a completely transparent manner (i.e. unmodified) to the
external device.
2) The external device recognizes the 20H character as a control character and sends the
40H character as acknowledgement.
3) The user receives the 40H character, interprets it as a control character and can now start
the data exchange. The user has thus adapted to the guidelines of the XYZ procedure and
created an identical procedure on his/her side.
The disadvantage of such an application is the relatively large amount of time involved. The
user must send a separate message frame for every control character. In the given example,
two message frames (20H and 40H) must be sent in addition to the actual message traffic.
3–14
Note for the user:
transfer.
PLC
20H
40H
XYZ
External device
© Siemens AG 1989 All Rights Reserved
06.91
6FC5 197-0AB20-0BP0
SINUMERIK 840/880 (PJ)
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