Siemens SIMATIC TIWAY 1 User Manual page 187

USING THE BDLC PROTOCOL
B.1 BDLC CONFIGURATION
BDLC is an unbalanced configuration meaning that there is one primary
station (the host computer) and one or more secondary stations (UNILINK Host
Adapters) as illustrated in Figure B–1. The primary is responsible for setting
each secondary to the normal response mode and for controlling the information
exchange.
Commands
PRIMARY
(Host Computer)
Responses
Secondary Secondary
Adapter Adapter
"A" "B"
Figure B–1 BDLC Unbalanced Configuration
In the normal response mode, a secondary station may only transmit frames as
a direct result of receiving permission from the primary. The primary grants
this permission by polling the secondary stations.
UNILINK HOST ADAPTER B–2
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