What restrictions are there with Industrial Ethernet CPs when the communications service ISO-on-TCP is being used in parallel via the open TCP/IP communication and the SEND/RECEIVE interface?
The following information applies only for the Industrial Ethernet CP 443-1 Advanced:
- 6GK7 443-1EX40-0XE0
- 6GK7 443-1EX41-0XE0
These modules support open TCP/IP communication via Industrial Ethernet using function blocks. In addition to the SEND/RECEIVE blocks (FC5/50 "AG_SEND/AG-LSEND" and FC6/60 "AG_RECV/AG_LRECV") you can also use the T blocks for the open TCP/IP communication via Industrial Ethernet.
|Order no.||Block name||Function|
|FB 63||TSEND||For transmitting data packets via an established communication connection|
|FB 64||TRCV||For receiving data packets on an established communication connection|
|FB 65||TCON||For establishing a communication connection|
|FB 66||TDISCON||For ending an existing communication connection|
This is high-performance communication which is used to exchange user data between two communication partners via the TCP/IP protocol. The connections using T blocks can be operated via the integrated PROFINET ports on an S7-CPU, as well as via the aforementioned Industrial Ethernet CPs.
If the open TCP/IP communication via Industrial Ethernet using T blocks is executed via communications processors, you can use ISO-on-TCP as communications service. Consequently, the RFC 1006 protocol extension is used on TCP/IP level. The CPU is the connection endpoint in each case. This marks a significant difference from communication via the SEND/RECEIVE interface in Industrial Ethernet CPs where the connection is configured in NetPro and the endpoint is always the CP.
Connections for open TCP/IP communication via Industrial Ethernet using T blocks are not configured in NETPRO; the connection parameters are specified in data blocks. These data blocks are transferred to the FB65 "TCON", which then establishes a communication connection. The connection parameters include the local and remote "TSAP (transport service access point)". This is defined by the following parameters.
- local_tsap_id (local TSAP)
- rem_tsap_id (remote TSAP)
The local and remote parameters are compared when a connection is established between the two partners. A communication connection is only established if the values match in pairs. The mechanism is used likewise for the configured connections for communication via the SEND/RECEIVE interface of the communications processors.
Restrictions with Industrial Ethernet CPs when the communications service ISO-on-TCP is being used in parallel using T blocks and the SEND/RECEIVE interface
The following conditions apply:
- Two connections are operated whose passive connection endpoint is in the station. The communications service ISO-on-TCP is used.
- Here, a connection is a configured connection for communication via the SEND/RECEIVE interface of the CP. Thus communication blocks FC50 "AG_LSEND" and FC60 "AG_LRECV" are used.
- The second connection is established with the function block FB65 "TCON" for the open TCP/IP communication via Industrial Ethernet using T blocks.
- The connection for the open TCP/IP communication via Industrial Ethernet is established by the user program after the CPU is started up.
- The connections are created as unspecified connections. This means that only the local connection parameters are preconfigured. The communication partner's connection parameters are not specified and are, thus, not evaluated when the connection is established.
In this case you should not configure the same TSAP for the configured connection for communication via the SEND/RECEIVE interface and for the connection using T blocks. If the same TSAP is configured for both connections, this leads to the CP, as an interface with the LAN (local area network), receiving two passive connection requests (or connection awaits) which are absolutely identical. However, the connection should be established once via the SEND/RECEIVE interface and once via the FB 65 "TCON".
Upon receipt, the CP first of all looks to see whether this connection attempt matches a configured connection for the communication via the SEND/RECEIVE interface. The CP only operates the connection-await function of the open TCP/IP communication connection via Industrial Ethernet using T blocks if this connection attempt is unsuccessful. If the same TSAP were to be configured for both connections, only the connection for communication via the SEND/RECEIVE interface would be established! Although the connection parameters for open TCP/IP communication via Industrial Ethernet using T blocks are specified correctly, this connection would not be established.
The following is defined in the documentation on the configuration of the parameter "rem_tsap_id" in the connection data block for the establishment of connections for open TCP/IP communication via Industrial Ethernet using T blocks:
|rem_tsap_id||Bits 0 to 4: slot,
bits 5 to 7: rack number
|Rack and slot of the remote connection endpoint (CPU)|
|rem_tsap_id[3-16]||TSAP extension||Further values on the more precise specification|
The first byte of the TSAP must always be configured 0xE0. This is specified for this type of connection.
It gives rise to the following recommendations:
- In configured connections for communication via the SEND/RECEIVE interface, the first byte of the TSAP should never be configured with 0xE0 or 0xE1. These identifiers are reserved and may, therefore, not be used.
- The likelihood of this error drops significantly if connection endpoints are created on a fully specified basis. Here, in addition to the local connection parameters, those of the communication partner are also checked when the connection is established.