Honeywell HPB User Manual page 25

HPB/HPA User Manual
Each HPB on a communication ring must have a unique address in order to individually receive commands
from the host processor. For example, if more than one HPB on a ring has a null address, and a 00 address
command is transmitted by the host, only the first null address HPB will receive the command and the
command is not passed on. This is the same for any address on a ring network.
Another advantage of the ring network is the ability to automatically assign device IDs to every HPB on the
network. Since commands flow through every HPB on the ring, a single *99ID=01 command will assign
ID=01 to the first unit, and each HPB in the ring will assign itself the next number. As the command is passed
along, each unit adds one to the ID command. For the example shown in Figure 4.12, the command will read
*99ID=07 when it returns to the host processor. The form of self-addressing will indicate the HPB position in
the communication ring relative to the host processor.
Every unit in the ring network has an assigned group address. When the host processor sends a group
addressed (*90 to *98) command, that command cycles through every HPB and is passed to the next one in
the loop. Those units having that group address read the command, then pass the command and reply to the
next unit in the ring. This is called a sequential response. Some sequential responses pass the string of
HPB replies before the group command while others pass the string of HPB replies after the group
command. See Table 5.3 for specific sequential command types.
Every unit in the ring network responds to a global addressed (*99) command. All units read the command
and pass the command and their response to the next unit in the ring. The sequential response is the same
as for the group command described above. See Table 5.3 for sequential command types.
24 www.honeywell.com