Device-Dependent Command Programming; 4-9-L Function (F) - Keithley 776 Instruction Manual

IEEE-488 Operntion
GET (Group Execute Trigger) - The GET command is
used to trigger or arm devices to perform a specific
measurement that depends on device configuration. Al-
though GET is considered to be an addressed command.
many devices respond to GET without being addressed.
Using the GETcommand is only one of several methods
that can be used to initiate a measurement cycle. More
detailed information on triggering can be found in Sec-
tion 3 of this manual.
To send GET command over the bus. the controller must
perform the following sequence
1. Set ATN true.
2. Address the Model 776 to listen.
3. Place the GET command on the data bus.
GET can also be sent without addressing by omitting
step 2.
4-94. Unaddress Command
The two unaddress commauds are used by the controller
to simultaneously remove all talkers and listeners from
the bus. ATN is low when these multiline commands are
asserted.
UNL (Unlisten) -All listeners arc removed from the bus
at once when the UNL commands is placed on the bus.
UNT (Untalk) - The controller sends the UNT command
to clear the bus of an)- talkers.
4-9-5. Device-Dependent Commands
The meaning of the device-dependent commands is de-
termined by instrumeut configuration. Generally. these
commands are seut as one or more ASCII characters that
tell the device to perform a specific function For esam-
ple. FO is sent to the Model 776 to place the instrument
in the FREQ A mode. The IEEE-488 bus treats device-
dependent commands as data in that ATN is high (false)
when the commands are transmitted.
IEEE-188 device-dependent commands are sent to
the Model 776 to control various operating conditions
such as display modify. operating mode. output and
parameter insertion. Each command is made up of an
ASCII alpha character followed by one ormore numbers
designating specific parameters. Foresample the output
waveform is programmed by send@ an ASCII "U"
followedby a number representing the output. The IEEE
bus treats device-dependent commauds as data in that
ATN is high when the commauds are transmitted.
A number of commands may be grouped together in
one string. The Model 776 will ignore all non-printable
ASCII characters (00 HEX through 20 HEX) escepl lhe
"CR" (carriage return). A command string is terminated
by an ASCII "CR" (carriage return) character (OD HEX)
which tells the instrument to cxecutc the command
string. recognized as end of command string.
If an illegal commaud or command paramelcr is
present within a command string. the instrument will:
1. Ignore the entire string.
2. Display appropriate front panel error message.
3. Se1 certain bits in its status byte.
4. Generate an SRQ if programmed to do so.
These programming aspects arc covered in tbc fol-
lowing.
NOTE
Before performing a programming
example. it is recommended that the
instrument be set to its default values
by seuding an SDC over the bus.
In order to send a device-dependent command. the
controller must perform the following sequence:
1. Set ATN true.
2. Address the Model 776 to listen
3. Set ATN false.
4. Send the command string over the data bus one byte
at a time.
NOTE
REN must be true when attempting lo
program the Model 776.
Commands that effect the Model 776 arc listed in
Table 4-S.
4-9. Device Dependent Commands
Programming
4-9-l. Function (F)
The function command sclecc the type of mcasurcnlcnt
made by the Model 776. The 13 parameters. which arc
associated with the function command. set the instru-
ment to measure one of these functions. The functiou
may be programmed by sending one of the following
commands:
FO=FRQA
Fl=FRQB
FZ=FRQC
F3=PERA
FJ = PLS A
FS = TI A to B
4-Y