Siemens SIMATIC S5 Manual page 111

Data Transfer with PLC-to-PLC Connections
Principle of Operation
Source PLC
Active network station
Status byte/SEND
to destination (A-NR)
(in the flag area)
o.k. to transmit?
yes
L2-SEND FB
Destination(A-NR ˆ = TLN)
Data
DB 51
DB 52
DB 53
Net data
1 to 242 bytes
LAN
bus
Figure 6-2. Functional Diagram of a PLC-to-PLC Connection
Explanations to Figure 6-2:
When there are no more jobs running on the PLC-to-PLC connection, the 'send' status byte
indicates that it is okay to transmit. L2-SEND is called up from the user program. L2-SEND receives
the following information from the parameter assignment:
• where to send the data (job number)
• where the net data are stored
The net data are transmitted to the addressed receiver via the network. At the receiver, a bit in
status byte 'Receive' indicates that the data arrived. The receiver can fetch the data by means of
L2-RECEIVE.
6-2
e.g., S5-95U
no
DB 50
Destination PLC
Active network station
Status byte/RECEIVE
to source (A-NR)
(in the flag area)
Receive viable?
yes
L2-RECEIVE FB
Source (A-NR ˆ =TLN)
Data
DB 60
DB 61
DB 62
DB 63
Net data
1 to 242 bytes
S5-95U, SINEC L2
e.g., S5-95U
no
EWA 4NEB 812 6112-02