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IEEE-488 PROGRAMMING
Programming
Examples
Throughout
the following paragraphs, numerous program-
ming examples show how to send the various commands
using two typical IEEE488 controllers: the Hewlett-Packard
Model 85 computer, and the IBM PC computer equipped
with a Keithley Model 8573 IEEE-488 interface. Note that
all these examples assume that the instrument's
primary
address is at its factory setting of 9. If you change the
primary address of the instrument,
you must modify the
various programming
examples accordingly.
In order to send a device-dependent
command,
the con-
troller must perform the following
sequence:
1. Set ATN true.
2. Address the Model 194 to listen. The actual listen com-
mand byte is derived by ORing the primary
address
with $20.
3. Set ATN false.
4. Send the command
string over the bus one byte at a
time.
NOTE
REN
must
be true
when
sending
device-
dependent commands to the instrument
or it will
ignore the commands and display a front panel
errOr message.
General HP-85 Programming
Example-Device-dependent
commands may be sent from the HP-85 with the follow-
ing statement:
A$ in this case contains the command letters representing
the command
string.
General
Model
8573 Programming
Example-Device-
dependent
commands can be sent from the HP-85 using
the following
statement:
Again, CMD$ contains the letters of the command string.
NOTE
Instead of typing
in complete programming
ex-
amples in this section in the direct mode, you can
use the example programs in paragraph 4.2.
4.9.1 Execute
(X)
The execute command
is implemented
by sending
an
ASCII "X" over the bus. Its purpose is to direct the Model
194 to execute other device-dependent
commands such as
F (function)
or R (range). Generally, the execute character
will be the last character in the command string; however,
there may be some cases where it is desirable to send a
string of command characters at one time, and then send
the execute character later on.
Commands
or command
strings
sent without
the X
character will not be executed at that time, but they will
be stored within
the command buffer for later execution
when the X character is finally received. Once the execute
command is finally
given, the stored commands will be
executed, assuming that all commands
are valid.
4.9.2 Function
(F)
The function
command
allows you to select the type of
mathematical
function
applied to the samples located in
the measurement
buffer. Options of the F command con-
trol such operating
modes as waveform,
TRMS
and
average, as summarized
in Table 4-9. Once all samples are
stored in the measurement buffer, the selected math func-
tion is performed
to form a reading. This reading is then
displayed and stored in the reading buffer at the present
cursor location,
if the reading
buffer
is enabled
(Q
command).
Upon power up, or after a DCL or SDC command,
the
instrument
will be in a mode determined
by the SETUP
1 configuration
(factory default, Fl average).
NOTE
When in the FO (waveform)
mode, individual
samples will
be transmitted
when
data is re-
quested over the bus. To cancel waveform output
after changing functions, either request all samples
in the measurement
or send a 80 command.
4-20
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