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These bus
commands
are subject
to
the constraints
of
the
4708
firmware.
The
instrument
will reject
and
ignore
invalid
com-
mands,
such
as
Remote
Sense
when
in
lOOmV
range.
Calibration
Enable
and
Calibrate
(W
and
C
codes)
These
are available for
automatic
calibration
of
the
4708, under
remote
control via the
IEEE
bus.
Refer
to
the Calibration
and
Servicing
Handbook.
W0
-
Calibration disable
W1
-
Calibration
enable
(only
if
CALIBRATION
ENABLE
keyswitch
set to
ENABLE).
C0
-
Calibration
Trigger
-
)
equivalent
to
CAL
key
)
Cl
-
As
SET
key
)
Refer
to
C2
-
As
STD
key
)
Section
1
C3
-
As ±0
key
(in
DC)
)
Programming
of
Bus
Transmissions
Output
string
Formation
The
4708
can be
commanded
to
output
'mtemaT
information
to
the
system
via the
IEEE-488
bus,
by
sending
one
of
the specified
'recall'
messages.
Only one
recall
command
should be included
in
a terminated
string.
As
well
as the
information
it
contains, the
string
needs
to
be
formatted
correctly for
acceptance
by
the system.
Many
variations
of format
are available; these
can be
programmed
for
the
type of
system
in
use.
The
length
and
construction
of
the
string
both
depend upon
the
type of information
to
be
transmitted,
and
thus
upon
the
codes
used
to
program
the
4708.
The
purpose of
this
explanation
is
to
describe the
effects
of
these
codes
on
the output
string
format
Figure
5.4
illustrates
the construction
of a
typical
string,
such
as
the
4708
output
value.
Notice
that
numerical
data
is
reduced
to
a
standard form,
and
scaled
by means
of an exponent
in
base
10.
All device
dependent messages use
the
ASCII
code.
Figure
5.4
Breakdown
of
a
typical
Output
String
(This
is
a
general
example
-
two
specific
4708
examples
appears
on page
5
-12)
1
byte
1
byte
Variable length
1
byte
1
byte
2
bytes
0or2
bytes
0or2
bytes
ASCII
space
Polarity
sign
Numeric
in
standard form
Polarity
sign
Exponent
delimiter
Legends
(optional)
Exponent
value
Terminators
(optional)
ASCII
'Space'
A
format
character
to
denote
the
beginning of an output
string
-
not present
for
recall
command
X8.
Polarity
Sign
Replaced
by
an
ASCII
space
in
AC
Functions.
For
DC
functions, the appropriate polarity sign
is
presented.
Numeric
sub-string
Length depends on
the resolution
of
the
information
to
be
transmitted,
and form depends on
the notation pro-
grammed
by
'L*
code.
Exponent
delimiter
'E'
Signifies that the
numeric
has
finished
and
the
next
three
bytes
form
the
exponent.
Exponent
Value
The
first
of
the three
bytes
is
always
*+
'
or
'
.
Because
the
value
is
never
greater
than
9,
the
second
byte
is
always
0,
and
the third
is
a
single
decimal
digit.
Legends
Inclusion
is
optional,
but
if
they are
programmed
in,
two
bytes are
always
present.
The
characters are appropriate
to the
programmed
state
of
the
4708.
Terminators
Two
terminating characters are
available,
as
programmed
by
'K' code.
The
EOI
bus
management
line
can
option-
ally
be
programmed
for
simultaneous transmission with
the
last
byte of
the
string.
5-10
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