Siemens SIMATIC TIWAY 1 User Manual page 15

OPERATION AND APPLICATION
Establishes communications
between the host computer
and the secondary devices.
Uses memory for:
Figure 2–4 Host Interface Unit Function
Part of the statistics memory area is used for a Secondary Log. As commands are
issued to connect and disconnect secondaries, the specified secondary address is
added or deleted from the Secondary Log and a network request is queued into
the Network Manager.
In the background, the adapter is continuously collecting statistics on the
number of commands processed, transactions completed on the network, and
other items. Commands to retrieve these statistics do not require network
transactions, but return the information from the appropriate statistical area.
The following operating modes include the HIU function.
D
Master Host Interface Unit (MHIU)
D
Host Interface Unit (HIU)
D
Master Host Interface Unit/Emulate Host Adapter (MHIU/EHA)
D
Host Interface Unit/Emulate Host Adapter (HIU/EHA)
HIU
Macro Buffers
(Dynamically allocated)
Host–to–Secondary Statistics
2–5 UNILINK HOST ADAPTER
USER MANUAL