HP 3468A - Functional Overview of HP-IL Devices

Functional Overview
Each device in the loop may possess one or more of the three basic device
capabilities: Controller, Talker, or Listener. The controller, as the name implies, has
the
responsibility
to
control
loop
activity.
The
-hp-
Model
41C/41CV
handheld
calculator
and
the
-hp-
Model
85
desktop
computer
are
examples
of
devices
which
can be used as controllers. They must, of course, be equipped with the proper in-
terface
module.
Controllers
transmit
all
commands
to
other
devices
in
the
loop
and
have Talker and Listener capabilities. The 3468A cannot serve as a controller. On-
ly one device in the loop may serve as a controller.
Talkers are devices that have the ability to send data or information (but not com
mands)
through
the
loop.
Note
that
a
talker
will
not
actually
send
its
data
or
infor-
mation
until
told
to
do
so
by
the
controller.
The
3468A
has
Talker
capabilities.
When
the
34682
is
talking
on
the
loop
its
TLK
annunciator
will
turn
on.
In
special
situations,
one
device
may
be
classified
as
a
Talk-only
device
and
sends
informa-
tion to Listen-only devices. Such a system would not have a controller. For exam-
ple,
the
3468A
can
be
configured
for
Talk-only
mode
and
send
measurement
results to a printer.
Listeners
are
devices
with
the
capability
to
receive
information
over
the
loop.
When
the
3468A
is
“
listening”,
its
LSTN
annunciator
turns
on.
Listeners
must
re-
main inactive until instructed
by the controller to receive the information.
Addressing
Each
device
in
the
loop
is
assigned
an
address
by
the
controller.
The
assigned
ad-
dress
will
probably
be
different
than
the
factory
preset
address.
The
3468A,
for
example,
has
a
preset
address
of
22.
If
the
3468A
is
the
only
device
in
the
loop
with
the
controller,
the
controller
will
assign
it
an
address
of
“1”.
The
address
permits
the
controller
to
specify
or
select
a
particular
device
in
the
loop
when
sen-
ding
commands.
Addresses
are
assigned
to
devices
sequentially
around
the
loop
in
the
direction
of
information
flow.
The
first
device
after
the
controller
is
assigned
an address of “1”. The second device is assigned the address “2”, and so on
around the loop.
Look at Figure A-1 again. The devices are shown with their basic capabilities, loop
address, and direction of information flow.
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