53Connection
Echochange - Manual / Connection
53
The S7-300 and 400 is usually addressed with the TSAP 03 02 (binary). The own TSAP is set to 01
01 by default.
S7-1200, S7-1500
The S7-1200 and 1500 is usually addressed with the TSAP 02 01 (binary). The own TSAP is set to
01 01 by default.
8.2.3.6 PLC Header
The data-stream oriented TCP/IP protocol is capable of grouping multiple short data
units into a larger unit. This increases the data throughput of the network. However, it
requires a header for the protocol above TCP. This corresponds to the procedure
common in other protocols (FTP, HTTP).
For this purpose, the 8-byte INAT PLC header was developed.
Only use the PLC header if the communication partner supports it. Otherwise, the
connection will fail!
PLC Header Format
Number of payload
bytes following the
header (LSB*).
Number of payload
bytes following the
header (MSB**).
Bit 0 = 1, if other
frames follow
*LSB: Least (Lower) significant byte
**MSB: Most significant byte
*** Bytes 2 / 3, bytes 4 / 5 and bytes 6 / 7 together form the “short” data value. They are represented in the INTEL format
Acknowledges
If DataLen equals 0, the frame does not contain payload, but a life data ack. Data acknowledgments
allow connection monitoring, a feature that TCP/IP, as a wide area protocol, does not include
inherently. The default times for connection monitoring are the same as for the H1 protocol. This
makes the S5 TCP/IP system H1-compatible from the PLC or PC perspective.
Sequence Numbers
Bytes 6 and 7 contain a sequence number that is 0 when establishing the connection and will be
incremented by 1 each time payload is sent. This frame counter additionally secures the data
transmission. If live data acks are sent, the sequence numbers are not incremented and Datalen is 0.
Fetch and Write Connections
For Fetch and Write jobs, the first 16 data bytes at the start of a job correspond to the SINEC AP
header. The SINEC AP header is also used for H1 communication.
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