20
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 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 4 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 4 for sequential command types.
Multidrop Network
The Multi-drop network consists of a three-wire bus (TD, RD, GD), as shown in Figure 11. A star network
configuration can also be used where each unit is connected directly to the TD, RD, GD terminals at the host
processor. The maximum number of addressable HPBs on a network is 89.
A HPB multidrop network connection of six units is shown in Figure 11. In this network, the device IDs are not in
order from one end of the network to the other. Ignoring their physical position on the network, the device IDs are
sequential beginning with ID=01 and without duplication. This is an important setup condition if response to global
commands (*99) is desired.
Figure 11. HPB Multidrop Network
Host Processor
ID=01
Group=9103
ID=02
Group=9101
ID=03
Group=9303
ID=05
Group=9102
ID=04
Group=9302
R5232
TTL
GD
TD
RD
GD
TD
RD
GD - Signal Ground
TD - Transmit
RD - Receive
GD
TD
RD
RS-232
TTL
GD
TD
RD
ID=06
Group=9301