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New
commands
are
executed
in this
sequence:
K
Output
terminator
format
L
Output
notation
Q
SRQ
Mode
W
Remote
Calibration
Enable
I
User Message
Input
00
OUTPUT
OFF
G
Guard
D
Safety
Delay
override
F
Function
R
Range
M
Main
Register
Value
(Output)
A
Full
Range/Zero
S
Sense
H
Auxiliary Register
Value
(Frequency)
T
Spot Frequency
01
OUTPUT
ON
G
Calibrate
Mode
P
Specification tolerance
U
Specification
limits
V
RecalVVerify
X
Diagnostic information
A
programmer
may
elect to
change
the
sequence
by
inserting
terminators
between
commands,
but
the
basic constraints
of
the
4708
will
still
be
imposed.
For example,
if
the function
is
changed
as
a
single
command
(e.g.
F3=)
the
main program
firmware
will set
Output
OFF
as a
result,
and
it
must
then
be
re-programmed
ON
by
the
user.
Succession
of Multiple
Commands
If
the input buffer
is
not
full,
new commands
are
accepted
to
await
their
turn for
processing,
and
are extracted
string
by
string.
The
input
system
design
makes
it
extremely
unlikely
that
the
buffer
will
overflow, unless
the
4708
is
in
Local
Control
and
the
command
input
is
excessive.
If this
does cause
the buffer
to
fill
up, the
4708
places
a hold
on
the
IEEE
bus handshake
sequence.
The
command IFC
can be used
to release the
hold,
followed
by
DCL
to clear the
4708
input
buffer;
but
as
a
general
principle,
this
situation
should
be
avoided
by
suitable
reprogramming.
Input Errors
Some
unwanted
commands
are ignored.
Others
enter the input
buffer
and
are rejected
later.
'Read'
commands
Before
addressing
the
4708
as
a
talker,
it
is
essential that
it
has
been
programmed
by
a
P,
U,
V
or
X
command.
Otherwise
it
will
have
no
data
to
uansmit.
Universal
commands
LLO
(Local
Lockout)
-
ignored,
no
capability.
PPU
(Parallel
Poll
Unconfigure)
-
ignored,
no
capability for
parallel poll.
SPE
(Serial
Poll
Enable)
-
sets
the
4708
to
serial
poll
state,
which
when
addressed responds with
the
RQS
status
byte.
This byte
contains the condition of the
request-
service
bit (bit 7).
If
the
4708
is
requesting
service;
bit
7
will
be
true,
the other
bits
describing the service
required.
SPD
(Serial
Poll
Disable)
-
returns the
instrument
to serial poll
idle
state.
Addressed
commands
PPC
(Parallel
Poll
Configure)
-
ignored,
no
capability.
GET
(Group Execute
Trigger)
-
ignored,
no
capability.
TCT
(Take
Control)
-
ignored,
no
capability.
GTL
(Go
To
Local)
-
instrument
returns
to
Manual
Control.
The
conU'oller
regains
remote
control
by
addressing
the
4708
as
a
listener
with
REN
line
true.
Clear
Commands
(DCL and SDC)
When
the
4708
receives
either
of
the
two
'Clear'
messages,
(DCL
is
universal
and
SDC
is
addressed
to
a
selected device)
it
will
default
to
the
predetermined
state
defined below.
During
the
time
taken
to default,
the
IEEE
interface
handshake
is
held.
These
commands
are effective
even
in 'Local' control.
A?
Not
Active
(see
M
code)
F0
DC
Volts
R0
Autorange
IV
default
M0
Where
value
is
zero
T0
Cancel Spot Frequency
H
(value)
Where
value
is
IkHz
G0
Local guard
S0
Local sense
O0
OUTPUT
OFF
state
Q0
SRQ
on
all
specified
states
D0
Safety delay
active
W0
Calibration disabled
C?
Not
active
-
disabled
by
WO
P?
Not
active
U?
Not
active
V?
Not
active
X?
Not
active
K*
Unchanged
L*
Unchanged
The
frequency
values held
in 'Store' volatile
memory
locations
F1-F5
are
reset to
the default
state
described
on page
3-8.
5-14
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