How The Send/Receive Interface Works On The Cpu - Siemens SIMATIC NET S7-300 Manual

4.1

How the SEND/RECEIVE Interface Works on the CPU

Functions (FCs)
The following functions (FCs) are available for handling communication on
connections:
S AG_SEND/AG_LSEND
This block takes the user data from the specified user data area and transfers it
to the Ethernet CP.
S AG_RECV/AG_LRECV
This block transfers received user data to the user data area specified in the
call.
The diagram below illustrates the situation. Using the FCs AG_SEND/AG_LSEND
and AG_RECV/AG_LRECV, the user program instructs the Ethernet CP to send or
receive data on the configured connection.
CPU
STEP 7
user program
User data areas
Figure 4-1 Interaction of the CPU and Ethernet CP on Connections
Amounts of Data
The Ethernet CP can transfer the amounts of data shown in the table below per job
on one connection:
Table 4-1
Sending
Receiving
S7-CPs for Industrial Ethernet Configuring and Commissioning
Release 01/2007
C79000-G8976-C182-07
4 SEND/RECEIVE Interface in the User Program
Ethernet station SIMATIC S7
CP
database
AG_SEND
AG_RECV
ISO Transport
8192 bytes
8192 bytes
Ethernet CP
User data
buffer
send
receive
ISO-on-TCP TCP
8192 bytes 8192 bytes
8192 bytes 8192 bytes
Communication
connection
UDP
2048 bytes
2048 bytes
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