HP 54501A - Protocol Exceptions

If
a
query
message
is
sent,
the
next message
passing
over
the
bus
should
be
the
<
response message
>.
The
controller
should
always
read
the
complete
<
response
message
>
associated
with
a
query
message
before
sending
another
<
program
message
>
to
the
same
instrument.
The
instrument
allows
the
controller
to send
multiple
queries
in
one query
message.
This
is
referred
to as
sending
a
"compound
query."
As
will
be
noted
later
in
this
chapter,
multiple queries
in
a
query
message
are
separated
by
semicolons.
The
responses
to each
of
the
queries
in
a
compound
query
will
also
be
separated
by
semicolons.
Commands
are
executed
in the
order
they
are
received.
This
also
applies
to
the reception
of
the
group
execute
trigger
(GET) bus
command.
The
group
execute
trigger
command
should
not
be
sent
in
the
middle
of
a
<
program
message
>.
Protocol
Exceptions
If
an error
occurs
during
the
information
exchange,
the
exchange
may
not
be
completed
in
a
normal
manner.
Some
of
the
protocol
exceptions
are
shown
below.
Addressed
to
talk with
nothing
to
say.
If
the
instrument
is
addressed
to
talk
before
it
receives
a
query,
it
will
indicate
a
query
error
and
will
not
send
any
bytes
over
the
bus.
If the
instrument
has
nothing
to say
because
queries
requested
were
unable to
be
executed because
of
some
error,
the
device
will
not
indicate
a
query
error,
but
will
simply
wait
to
receive
the
next
message from
the
controller.
Addressed
to
talk
with
no
listeners
on
the
bus.
If
the
instrument
is
addressed
to
talk
and there
are no
listeners
on
the
bus,
the
instrument
will
wait for
a
listener to
listen,
or
for
the
controller
to
take
control.
HP
54501A
Programming
Message
Communication
and System
Functions
3-3