Data Transmission by Accessing Layer 2 Services S5-95U, SINEC L2
SAPs and Job Numbers
The communications processor has buffers for the data to be sent and the data received. These
buffers are referred to as SAPs (Service Access Points to layer 2)
An SAP is addressed by assigning it a number. You have the SAPs with the numbers 33 to 54 and
64 (default SAP) at your disposal for invoking layer 2 services. To enable a SAP to be referenced
from the STEP 5 program, a layer 2 access must be configured for it. You define the SAP number
in DB1 for this purpose ( section 8.3)
The interaction between STEP 5 programs and SAPs is explained in Figure 8-3. Figure 8-3 is
explained on page 8-7.
Figure 8-3. Using Job Numbers (A-NR) for Accessing Layer 2 Services via SAPs
LAN
bus
Sending PLC (active)
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Request via L2-
SEND, e.g. via
A-NR 33
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Confirmation via
L2-RECEIVE and
A-NR 33
DB1
STEP 5
program
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SINEC L2
interface
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Communications
processor
SAPs
Control
processor
64
33
54
Receiving PLC (active or passive)
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Indication via
L2-RECEIVE, e.g.
via A-NR 154
DB1
STEP 5
program
SINEC L2
interface
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Communications
processor
SAPs
Control
processor
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64
33
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8-6
EWA 4NEB 812 6112-02
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