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OPERATION AND APPLICATION
2.9 BASIC NETWORK OPERATIONS
The simplest network operations, in either a single or multiple host network,
are performed using the Base HIU commands, codes 1–8. These commands
allow you to bring secondary devices online and offline, send data to/from the
secondaries, and retrieve basic statistics. However, these commands are direct
issue requests, meaning that the host application must wait for the network
response before another command can be issued. Paragraph 2.10 discusses how
to process multiple outstanding transactions.
2.9.1
Bringing Secondary Devices Online
Issue the CONNECT SECONDARY command to bring secondary devices
online. This command logically connects one or more secondary devices and
allows your applications software to selectively connect the secondary devices
on the network. Memory space will be allocated for secondary device statistics
the first time that the secondary is connected. This space will remain in use
until the adapter is reset.
The address value FF hex or 255 decimal has been reserved as a global address
that will connect all secondaries up to the largest address value, specified when
the adapter was configured. You must be careful when requesting multiple
secondary connections. If the responses are not received before the host
command timeout, the ERROR RESPONSE will be returned and you will have
to issue the READ SECONDARY LOG command to determine which
secondaries were connected before the timeout. A successful connection will
return the command code and a list of the secondary device addresses that were
connected successfully. If no address in the list was connected, the response will
be the command code and a 00 address value.
The host computer must wait for the response to be
returned for the CONNECT SECONDARY and
READ SECONDARY LOG commands before issuing
another command, regardless of the adapter
operating mode. There can be a long time delay when
using the special global address (FF hex).
NOTE
2–25
UNILINK HOST ADAPTER
USER MANUAL
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