S5-95U, SINEC L2 Data Transmission by Accessing Layer 2 Services
8.7 Holding Data for Fetching Once Only by a Station (RUP_SINGLE
Service)
The RUP_SINGLE (Reply UPdate SINGLE) service is used for holding data for fetching in an
active or passive station. The data held can be fetched by an active station once only, using the
SRD service ( section 8.9).
Before the sender requests data from the receiver (SRD layer 2 service), the receiver must keep
the data ready in an SAP.
The receiver uses either the RUP_SINGLE or RUP_MULTIPLE service to do this ( section 8.8).
The RUP_SINGLE service holds the requested data ready for once-only fetching. If an active
station requests data cyclically, this guarantees that it always receives new data.
Reason : Once the sender has read the data out of the SAP, the latter is empty. When the SAP is
empty, i.e. no new data are yet pending, the sender receives a confirmation header
(SRD layer 2 service).
New data are written into the SAP at the next RUP_SINGLE or RUP_MULTIPLE.
Data holding procedure for the receiver ( Figure 8-10):
The request (header + net data to be held ready for fetching) in the flag or data area is sent
with L2-SEND (request to layer 2).
The 'Send' status byte informs the receiver that a confirmation has been transmitted, and the
receiver fetches the confirmation (= header) with L2-RECEIVE.
Figure 8-10. Holding Data Ready for Fetching with the RUP_SINGLE Service
SAP
LAN bus
Receiver control program (Station 2 in the
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(Data)
SEND
RUP_SINGLE
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Request
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STBS:...2
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Confirmation
Confirmation
header, 8 bytes
In example: DB33,
DW 10 to DW 13
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STBS:...4
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RECEIVE
As soon as the data are read out of the
SAP, the SAP can be refilled with data
(otherwise the sender will not receive any
data the next time it attempts to fetch them).
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STBS:...3
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Request header
8 bytes
ID: 06
H
In example: DB33,
DW 1 to DW 4
Data
In example: DB33,
DW 5 to DW 8
Sender control program (Station 1 in the
The data are fetched by the
sender with the SRD service.
The receiver then gets an
indication, which it must fetch
with the L2-RECEIVE
( 8.9).
S5-95U
S5-95U
Since the receiver sends data to itself with the RUP_SINGLE service, you must specify the same
SAP in DB1 for sending and receiving ( section 8.3). The destination SAP in the request header is
irrelevant.
Figure 8-11 shows the request and confirmation structures for the RUP_SINGLE service.
EWA 4NEB 812 6112-02
8-23
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