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SECTION 4
GPIB Interface
Delimiter
The Model 3930A recognizes <CR>, <LF>, or <EOI> in
any combination
as a delimiter for receiving code strings
in the listener mode.
The delimiter used when sending a response in the talker
mode is set from the front panel with the GPIB key. Only
<CR> or <CR><LF> can be selected as an output delim-
iter, and EOI is sent simultaneously.
For information
on
delimiter
selection, see
0
8
in paragraph 3.2.1. The fac-
tory default delimiter
is <CRxLF>
h EOI.
Response to Interface Messages
Table 4-4 summarizes
Model 3930A responses to inter-
face messages.
Table 4-4.
Response
to Interface
Messages
IFC
DCL
and
SDC
LLO
GTL
Initializes
GPIB interface.
Releases specified listener and talker modes.
Clears GPIB input/output
buffer.
Clears error status.
Releases SRQ transmission
and resets SRQ
causes (unit's operating modes do not
chance).
Disables front panel LOCAL key.
-I
Goes into local mode (front panel program-
ming enabled).
Program Codes
Program codes used for the various settings of the Model
3930A are temporarily
stored in the input buffer as re-
ceived. When a delimiter is received, they are interpreted
and executed in the order received. The input buffer can
store up to 128 characters (128 bytes). Note that space,
tab, null, semicolon,
and delimiter
characters are not
stored in the input buffer.
When more than 128 program code characters are re-
ceived, the input buffer overflows. When an overflow OC-
curs, the input
buffer is cleared, and program
codes
stored in the buffer are not executed.
In addition,
the input buffer is cleared, and subsequent
program codes are not executed when an illegal header
or parameter is found during the interpretation
of a pro-
gram code.
When interpretation
and execution are completed, the in-
put buffer is cleared, and the unit is ready to receive the
next program code.
As shown in Figure 44, program
codes consists of a
header and a parameter. More than one program code
can be sent at a time, up to a maximum
of 128 characters.
Multiple
program codes can be separated by a space or
semicolon (;) to improve readability.
There are two general types of program codes: parame-
ter-setting
messages and inquiry
messages. Parameter-
setting messages are used for setting parameters or for
sending
operating
instructions.
Inquiry
messages are
used for requesting state and parameter setting inforrna-
tion from the instrument.
Parameter Setting Messages
The format of a basic setting message is shown below. In
this example, the frequency is set to l.OHz,
and the am-
plitude is set to l.OVp-p.
a: Indicates the three-letter alphabetic character header.
Either upper-case or lower-case letters can be used.
b: Indicates
a space character inserted for readability.
There is no limit on the number of spaces, and the
space can be omitted. Space, tab, null, and semicolon
characters are ignored and are not stored in the GPIB
input buffer.
4-7
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