Technical data

Transmitting data with request to receiver to return data (service: SRD)
Sequence of the transmission:
Before the sender requests data from the receiver, the receiver must
prepare the requested data in a CP buffer (responder function). The
receiver either uses the "reply update single (RPL_UPD_S)" or the "reply
update multiple (RPL_UPD_M)" service.
The RPL_UPD_S service prepares the requested data once. After the
requesting station has read the data from the buffer the buffer is empty and
must be filled again with an RPL_UPD_S service. The user is informed that
the data have been fetched in the SRD indication (link_status). If the
requesting station finds an empty buffer, it is informed by an error message
in the confirmation header (link_status).
Control program sender
S5 add.
ANZW
ANR
SSNR
PAFE
CP
Anzw = Job_active receive possible
Anzw = Job_active
(data)
CP
BUS
FB
SEND
Anzw = RECEIVE possible
SDN-
Request
e.g..:DB
Header
DATA
(...2
(...1 or
(...5
if previously
(...4
(...3
S5 add.
ANZW
ANR
SSNR
PAFE
FB
RECEIVE
e.g..:DB
Header
DATA
S5-Adr.
ANZW
ANR
SSNR
PAFE
FB
RECEIVE
e.g.:DB
Header
Anzw = Job_complete_without_error
(...4
(...4
1
2
4
3
5
H
)
H
)
H
)
H
)
H
)
H
)
H
)
Control program receiver
Anzw = Job_complete_without_error
B
U
F
F
E
R
Fig. 8.8 Transmitting and Receiving Data without Acknowledgment (Service: SDN)
Free Layer 2 Communication B8976060/02
Volume 1 8 - 22