The S5-compatible communication is the most frequently used communications service for transferring user data via Industrial Ethernet CPs. In addition, there are communication blocks that have to be called in the S7 program of the CPU.
The communication block FC50 "AG_LSEND" is used for sending data and communication block FC60 "AG_LRECV" is used for receiving data. These communication blocks are used for data exchange via the following connection types:
- ISO-on-TCP connection (RFC1006)
- TCP connection
- UDP connection
- ISO Transport
From CP443-1EX20 (6GK7443-1EX20-0XE0) onwards that are additional communication blocks for data exchange via the above-mentioned connection types:
- FC53 "AG_SEND"
- FC63 "AG_SRECV"
This is a more powerful communications option. Compared with the S5-compatible communication with FC50 "AG_LSEND" and FC60 "AG_LRECV", there is an increase in performance by a factor of up to 3 depending on the plant constellation.
Configuration of the S5-compatible communication with FC53 "AG_SSEND" and FC63 "AG_SRECV":
For S5-compatible communication via Industrial Ethernet, you can use the following operating modes in CP443-1EX20 (6GK7443-1EX20-0XE0) onwards:
- SPEED Send/Recv
- Fetch Passive
- Write Passive
The "Send/Recv" operating mode is enable by default. To use the faster communication with FC53 "AG_SSEND" and FC63 "AG-SRECV" you must select the "SPEED Send/Recv" mode in the "Options" tab of the Properties dialog of the communication connection configured.
Fig. 01: Properties dialog of the communication connect - "Options" tab
Furthermore, in the STEP 7 Hardware Configuration, the extended address range must be enabled in the Properties dialog of the Industrial Ethernet CP. For this you open the Properties dialog of the Industrial Ethernet CP, select the "Addresses" tab and enable the option "Address setting for LOCK/UNLOCK with FETCH/WRITE, SPEED Send/Receive". Now the module occupies 64 peripheral input addresses and 64 output addresses.
Fig. 02: Properties dialog of the Industrial Ethernet CP -> "Addresses" tab
Operating modes Send/Recv and SPEED Send/Recv use the same resources pool on the IE CP. An IE CP of SIMATIC S7-400 supports 64 connections for S5-compatible communication. You can define how many of these connections are to operated with the Send/Recv and SPEED Send/Recv modes. The only important thing here is that the CPU has enough free S7 connection resources.
Maximum length of the user data to be transferred:
If you are using the SPEED Send/Recv mode, you can transfer a maximum of 1452 bytes of user data. User data transfer with the Send/Recv mode depends on the connection type used.
||Data length for Send/Recv with FC50/60
||Data length for SPEED Send/Recv with FC53/63|
Occupied connection resources:
The communication processors support communication connections always in parallel for S5-compatible communication and S7 communication. For one configured connection, only one resource is occupied in the IE CP for S5-compatible communication. The number of S7 connections supported in the CPU does not depend on this.
This changes if you configure a communication connection with the SPEED Send/Recv mode. In this case, one Send/Recv resource and one S7 connection resource per connection are occupied in the CP IE. In addition, one S7 connection resource is likewise occupied in the CPU.
||SPEED Send/Recv mode|
|Send/Recv connection resource in the IE CP
|S7 connection resource in the IE CP
|S7 connection resource in the CPU
Length of the data buffer for FC63 "AG_SRECV" with TCP connections:
Die folgende Vorschrift gilt nur für TCP-Verbindungen.
When receiving data packages, the receive buffer must always be called with the maximum data length of 1452 bytes. This rule also applies when you are receiving just a few bytes.
In the case of TCP connections with the SPEED Send/Recv mode, the transfer of data packages from the LAN (local area network) to the user program is structured so that always the number of bytes actually available are transferred to the CPU. Therefore, if an IE CP receives a data package of 10 bytes every 5s, for example, the data is first collected in the IE CP. If the user program then calls an FC63 "AG_SRECV" on the relevant connection after 20s, all the bytes collected until then are transferred all at once to the CPU. In the case described, this would be 40 bytes (4 * 10 bytes). In the case of a TCP connection, it is not possible to provide information about how many data packages constitute the data received and where the message limits lie. This can only be achieved by structuring the user data.