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OIT***-F113-B12-CB*
Communicating with the OIT system
The PLC determines which data set matches the input data and sends it to
the OIT system together with the message "Current data to OIT" (SAH 2). If
the PLC does not find a matching data set for the data input from the OIT
system, the PLC will send the message "No data to OIT" to the OIT system
(SAH 3).
This will end the complete read cycle.
7.2
TCP/IP communication (as per RFC1006 standard)
RFC 1006 (ISO Transport service through TCP) is a protocol extension of the TCP
protocol. In addition to the TCP data, further information is transmitted between
the participants in order to provide certain services to the operator. Data transfer
normally takes place data-oriented over the TCP protocol. Neither information on
the length nor information on the beginning or end of a communication is
transmitted. This cannot be used in automation technology. Here, specific data
packets that indicate length, beginning, and end must be used. Data transfer
takes place message-oriented with RFC1006. Thus, only closed message blocks
are sent through a connection and are recognized as such by the receiver. RFC
1006 now specifies which information must be added to the transmitted data in
the form of a header in order to ensure this. So RFC 1006 makes message-
oriented transmission available to applications set up on the data–stream oriented
TCP protocol.
The TCP/IP protocol enables communication between the PLC and OIT system.
For communication as per the RFC1006 standard, a block of 7 bytes, structured
as follows, gives access to the data telegram.
Byte
hex
The telegram blocks that attach to the RFC1006 block are created without
RFC1006, in accordance with the telegram definition, (see chapter 7.1), so that
the following sizes for data telegrams result as per the RFC1006 standard:
Data telegram orientation
SPS -> OIT
OIT -> SPS
0
1
2
0x03
0x00
0x00
RFC1006 header
3
4
0xEB
0x02
TSAP header
7 bytes
Data telegram length
max. 561 bytes
35 bytes
5
6
0xF0
0x80
31
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