Siemens SINEC L2 User Manual

S5-95U, SINEC L2 Data Transmission by Accessing Layer 2 Services
8.6 Sending Data to Several Stations (SDN)
The SDA (Send Data with No Acknowledge) layer 2 service is used if an active station is to send
data to several active or passive stations (multicasting).
Data can also be sent to one active or passive station with the SDN service. However, SDA is
better suited for this ( section 8.5).
SDN has the following disadvantage compared with SDA:
The confirmation received by the sender contains no information on whether the data have been
correctly received or not. The sender only receives confirmation from its local communications
processor that the data have been sent off properly.
Prerequisites for multicasting:
• You must assign the same receive SAP in the DB1s of all receiving stations ( section 8.3).
• You must enter the global address for multicasting "127" in byte 6 of the request header.
Data transmission schematic ( Figure 8-8):
The request (header + net data to be transmitted) in the flag or data area is sent with L2-SEND
(request to layer 2).
The 'Receive" status byte informs all receivers that an indication has arrived.
Each receiver fetches the indication (header + net data received) with L2-RECEIVE.
The 'Send' status byte informs the sender that a confirmation has been transmitted.
The sender fetches the confirmation (= header) with L2-RECEIVE.
Figure 8-8. Sending and Receiving Data without Acknowledgement or Confirmation (SDN)
LAN Bus
Request SDN
Header with 8 bytes
In example: DB33,
DW1 to DW4
Data
In example: DB33,
DW 5 to DW 8
a a a a a a a a a a a a
a
a a a a a a a a a a
a
a
a a a a a a a a a a
a
a
a a a a a a a a a a
a
a a a a a a a a a a a a
STBS:...2
H
SEND
SDN request
a a a a a a a a a a a a
a
a a a a a a a a a a
a
a
a a a a a a a a a a
a
a
a a a a a a a a a a
a
a a a a a a a a a a a a
STBS:...4
H
Confirmation header
8 bytes
In example: DB33,
DW 10 to DW 13
RECEIVE
Request
(Data)
Sender control program (Station 1 in the
a a a a
a
a a
a
a
a a
a
a
a a
a
a a a a
a a a a
a
a a
a
a
a a
a
a
a a
a
a a a a
a a a a
a
a a
a
a
a a
a
a
a a
a
a a a a
(acknowl-
edge)
a a a a a a a a a a a a a
a
a a a a a a a a a a a
a
a
a a a a a a a a a a a
a
a a a a a a a a a a a a a
STBR:...4
H
a a a a a a a
a
a a a a a
a
a
a a a a a
a
a a a a a a a
(Data)
Indication header
8 bytes
In example: DB34,
DW 10 to DW 13
Data
In example: DB34,
DW 14 to DW 17
RECEIVE
STBR:...1
H
a a a a
a
a a
a
a
a a
a
a
a a
a
a a a a
a a a a
a
a a
a
a
a a
a
a
a a
a
a a a a
a a a a a a a a a a a
a
a a a a a a a a a
a
a a a a a a a a a a a
Indication
a a a a a a a a a a a a
a
a a a a a a a a a a
a
a
a a a a a a a a a a
a
a a a a a a a a a a a a
STBS:...3
H
a a a a a a a a a a a a a a a a
a
a a a a a a a a a a a a a a
a
a a a a a a a a a a a a a a a a
Confirmation
Receiver control program (Station 2 in the
S5-95U S5-95U
EWA 4NEB 812 6112-02 8-19

Siemens SINEC L2 Specifications

General

Brand	Siemens
Model	SINEC L2
Category	Controller
Language	English