Siemens SIMATIC TIWAY 1 - Manual (Page 83)

THE TIWAY I NETWORK PORTS
UNILINK HOST ADAPTER 4–9
USER MANUAL
4.3 TIWAY I HDLC NETWORK PROTOCOL
The TIWAY I network uses the HDLC protocol in the unbalanced, normal
response mode (UNRM) for transmission of commands and responses. In this
mode a single Network Manager (primary) controls the flow of messages
between secondary devices. Information flows between the primary and
secondaries inside HDLC I-Frames or information frames. The destination of
the frame is specified by the address field, the nature of the frame by the control
field, and any data specified by the information field. The TIWAY I primitive
requests and responses are encapsulated inside HDLC I-Frames according to
the format shown in Figure 4–6.
Flag Address Control Information FCS Flag
Figure 4–6 HDLC Frame