HP 54501A - Message Communication and System Functions; Protocols; Functional Elements

Message
Communication
and
System Functions
3
This
chapter
describes
the
operation
of
instruments
that
operate
in
compliance
with
the
IEEE
488.2
standard.
Instruments
that
are
compatible
with
IEEE
488.2
must also
be
compatible
with
IEEE
488.1,
however
IEEE
488.1
compatible
instruments
may or
may
not
conform to
the IEEE 488.2
standard.
The
IEEE 488.2
standard
defines
the
message
exchange protocols
by which
the
instrument and
the
controller
will
communicate.
It
also
defines
some
common
capabilities,
which
are
found
in
all
IEEE
488.2
instruments.
This chapter
also
contains
a
few
items
which
are
not
specifically
defined
by
IEEE
488.2,
but
deal with
message
communication
or
system
functions.
Protocols
Functional Elements
The
protocols
of IEEE 488.2
define the
overall
scheme
used
by
the
controller
and
the
instrument
to
communicate.
This
includes
defining
when
it
is
appropriate
for
devices
to
talk
or
listen,
and what
happens
when
the
protocol
is
not followed.
Before
proceeding
with
the
description
of
the
protocol,
a
few
system
components
should
be
understood.
Input
Buffer.
The
input
buffer of
the
instrument
is
the
memory area
where
commands
and
queries
are
stored
prior
to
being
parsed
and
executed.
It
allows
a
controller to
send
a
string
of
commands
to
the
instrument
which
could
take
some
time to
execute,
and
then
proceed
to
talk
to
another
instrument
while the
first
is
parsing
and
executing
commands.
The HP
54501A's
input
buffer
will
hold
300
characters, or
bytes
of
data.
HP
54501A
Programming
Message
Communication and System Functions
3-1