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SECTION 4
GPIB Interface
Inquiry
Messages
An inquiry
message is a special program code with a
question mark (?) located at the beginning.
An inquiry
message is used to request information
from the instru-
ment regarding
a state or particular
parameter setting.
Except for special cases, each inquiry
message corre-
sponds to an equivalent
parameter-setting
message. In-
quiry messages include only the header and a question
mark; no parameters are used.
After receiving
an inquiry
message, the Model 3930A
searches for the corresponding
setting and places the re-
sponse in its output buffer. When it is addressed to talk, it
sends that setting information
to the controller.
The response output format is the same as the format of
the
corresponding
setting
message,
as shown
in
Figure 4-5. The format for inquiries without
correspond-
ing messages are discussed below.
@we 4-5.
Response Output Fomt
When more than one inquiry
is sent to the Model 3930A
at the same time, only the last request is accepted, and
previous requests are ignored. When a new inquiry
is re-
ceived before the response for a previous request is com-
pleted, the new request over-rides the previous request.
NOTES:
1. The header in the inquiry
response string can be
turned on or off by sending the command "HDR 1"
or "HDR
0" respectively.
The power-on
default
header state is header on ("HDR 1").
2. Either <CR><LF>"EOI
or <CW"EOI
can be se-
lected as the inquiry
response delimiter.
The d&r-
iter can be progmmmed
with the front panel GI'IB
key; see
0
8
in paragraph 3.2.1. The factory default
delimiter
is <CR><LF>"EOI.
Numeric Format of Inquiry
Message Response Parame-
ters
As described below, three different formats are used for
inquiry
response parameters.
NRl Inquiry
Response Format
DDDD
--
I
I
Lk
Numeric digits
l
Space indicates plus sign is assumed
.
The number of digits for each infor-
mation item are fixed.
Example:
FNCI
(Indicates
the output
waveform
is 'L
Header: three characters, space indicating
sign: one character, numeric parameter: one
character. Total: five characters.)
NR2 Inquiry
Response Format
In the NR2 format, inquiry
response parameters
are
specified as real numbers:
DD.DD
I
I
k
.
Numeric digits with decimal point.
.
Space represents plus, and minus
sign (-) indicates negative values.
.
The decimal point is always included.
.
The number of parameter characters
for each information
item is fixed.
Example:
DTY 25.0
(Indicates that the square-wave duty cycle is
set to 25%. Header: three characters, space
indicating
sign: one character, numeric pa-
rameter including
decimal point: four char-
acters. Total: eight characters.)
4-9
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