Marconi Instruments 2955 - Page 68

I
OPERATION
Display
annunciators
During
GPIB
operation, the
following
announcements are
made on
the
screen:-
Remote:
Once
the
instrument
has
received a remote
enable
and has
been addressed,
it
will
enter
the
remote state.
This is
annunciated
by REM
appearing in
reverse field
in the
bottom
right-hand
corner
of the screen.
Addressed: When
in the remote
condition
and the
instrument
is
addressed to
either
talk
or
listen,
this
is annunciated by
ADR appearing
in
reverse
field in the
bottom
right-hand
corner
of
the
screen.
Service
request:
When
in the
remote
condition
and
enabled, a
serv'ice
request is
raised,
this
is
annunciated
by SRQ
appearing in reverse
field in the
bottom
right-hand corner of the
screen.
Local; When
in
the
remote condition
and Local
Lockout
(LLO)
has not been
sent, this
is
annunciated by
LCL appearing next
to the HELP
key.
Pressing HELP
will
then
cause
the
instrument
to enter a
Go To Local
(GTL)
condition.
Note
that the Go To
Local condition is not the same as the
power-on condition since the re.mote
enable
(REN)
line
from
the
controller
will
still
be
active.
GPIB
commands
Commands take the
form of a
two-character
alphabetic pair
which may
be
followed
by
amplifying,
non-exponential
numeric
data.
Separators are
required for
multiple
data and
for
multiple
commands
forming
a
string.
Command
format
This
lakes the
form
of <HEADER>
<DATA>
<TERMINATOR'SEPARATOR>
<HEADER>
-
A
two-character
command
identifier.
<DATA>
-
In
form NRI (integer) or
NR2 (fixed
decimal
point),
i.e.
exponential formats are
not allowed.
Where there
is
more than one item of
data,
separators
must be
used.
<TERMINATOR/SEPARATOR>
<;>
<.xCR>
<LF> <ETX>
<ETB>
<EOI>
<space>
Used
to
delimit commands
in command
strings. Can
be
omitted if unambiguous.
Command
separators.
Command string
dclimiters/tcrminators,
Note that
<EOI>
must only be sent
with
the
last
character.
ignored by
the 5vstc.m-u:>ed for
in
tell
ig:bi!it>
only.
The
example which
follows
shows
the format of a command
string
where
the
data
items arc
separated bv
commas,
the
command.s
arc
delimited bv semicolons
and the strina is
terminated
bv
EOL-
P04U.3
;
P04
1.5 ; <
EOf>
-
POke
3
and
5
to memory
locations
40
and
4
1 respectively.
Notes...
(
1)
Certain
commands
cause
the instrument to
output
more
data
than it can store
in
its
output
buffer,
c.g.
SV
and
RD39. see
‘Non-keyboard
commands'
below.
The result
is
that
the
data
is
held off from
entering
the
buffer
and
hence
the
instrument
stops.
To
prevent
locking
up the instrument, a
3
second
timeout takes effect. If data
output
has not
been
started,
or
is
read
out
slower
than
i
character per 2
seconds, then a buffer
overflow
error
is
raised
and
the
instrument
aborts the
command.
(2)
The
input buffer
Icncth
is
128
characters. If
the buffer
overflows, then the
GPIB
is
held oft
until
further
space
is
available.
If
however,
the buffer
does not
contain a
command
delimiter
then
the
data
is
lost
and
an
error
is
raised. This is because
command
interpretation,
and
hence
buffer
unloading,
does not
occur
until a
command string delimiter is
received.
3
->44
46881-622N
Apr.
88