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4.7 HPB Addressing
The HPB provides three levels of addressing. The lowest level of address is the individual unit address, or
device ID
.
This address level is used to address any single HPB. The next level is
group
address, which is separate from the
device ID. All HPB units with the same group address will respond to a command sent to this level address. The last
is a
global address
, which is read by all HPBs on the network. The device ID can be assigned by direct command or
assigned automatically based on its position from the host processor in HPB network. The
null address
(00) is simply
a default device ID that the HPB automatically assumes until one is assigned. That is, upon power-up, if there is no
ID assigned, and an ID has not been stored in the EEPROM, then the HPB will assign itself the 00 null address.
The individual unit address, or
device ID
, has an assigned range from 01-89. The null address 00 is the factory default
address for unassigned HPBs. A unit with the null address, replies with a null address header. The null address
header characters are ? for ASCII format or ^, &, |, or % for binary format (see Section 5.5 for these format types). A
unique device ID allows the host processor to send commands to specific units on a bus.
The second level of addressing is a multicast, or
group
, address in the range of 90-98. Each unit can be assigned a
group address by the ID command. A unit responds to its group address in the same manner as it does to its global
address described below. The group addressing allows the host processor to send commands to several units having
the same group address. The factory default group address is 90.
The highest level of addressing is the broadcast, or
global
, address 99. All units receive global addressed commands.
All ring networked units respond to global commands. Only multi-drop units with assigned addresses will respond
to global commands. A multi-drop unit with a null address will not reply to any global command. The global address
is not assigned but is built into the HPB.
Ring Network
The ring network consists of a three-wire bus (TD, RD, and GD) that begins and ends at the host processor. The
maximum number of HPBs with assigned device IDs on a network is 89.
An HPB ring network connection of six units is shown in Figure 10. In this example, the Device IDs are sequential,
starting from 01, from the transmit port of the host processor around the loop. There are two address groups, 91 and
93; each have 3 HPB units assigned. (Note: A TTL-to-RS232 converter is required for connection to the host
processor.)
Figure 10. HPB Ring Network
GD
TD
RD
Host Processor
Signal Ground
GD - Signal Ground
TD - Transmit
RD - Receive
TD
RD
TD
RD
TD
RD
Signal Ground
ID=01
Group=91
ID=03
Group=93
RD
TD
RD
TD
RD
TD
ID=06
Group=93
ID=05
Group=91
RS-232
TTL
GD
TD
RD
ID=04
Group=93
ID=02
Group=91