Siemens SIMATIC S5 Manual page 160

Data Transmission by Accessing Layer 2 Services
Figure 8-9 shows the request, confirmation and indication structures for the SDN service
Request
Byte
0 com_class
FDL_Request=00
1 user_id
User-definable ID
2 service_code
Type of service requested:
SDN=01
H
3
irrelevant
4 Bits 4 to 7
service_class
Priority of
send frame
low=0 or
H
high=1
H
5 Destination SAP 0 to 62,
FF (=default SAP 64)
6 rem_add_station
Address of the destination
station (1 to 126 or 127 for
multicast)
7 rem_add_segment
Logical segment address;
always enter FF
8 .
Send data
. .
(0 to 242 bytes)
249
Must be specified by the user in the request header
Figure 8-9. Structure of Requests, Confirmations and Indications for the SDN Service
8-20
Byte
0
H
1
ID assigned in connection with
2
3
4 Bits 4 to 7
Bits 0 to 3
0 service_class
Priority of the
send frame
low=0
high=1
5 Destination SAP 0 to 62,
FF (=default SAP 64)
6
Address of the destination
7 rem_add_segment
Logical segment address;
H
Confirmation
com_class
Confirmation=01
H
user_id
a request
service_code
Type of service:
SDN=01
H
link_status
( Table 8-6 )
Bits 0 to 3
0
or
H
H
rem_add_station
station (1 to 126)
is always FF
H
S5-95U, SINEC L2
Indication
Byte
0 com_class
Indication=02
1
irrelevant
2 service_code
Type of service: SDN=01
SDN =7F
Multicast
3
irrelevant
4 Bits 4 to 7
service_class
priority of
receive frame
low=0 or
H
high=1
H
5 Source SAP 0 to 62,
FF (=default SAP 64)
6 rem_add_station
Address of source station
(1 to 126)
7 rem_add_segment
Logical segment address;
is always FF
8 .
Receive data
. .
(0 to 242 bytes)
249
EWA 4NEB 812 6112-02
H
or
H
H
Bits 0 to 3
0
H