Keithley 194 Instruction Manual page 105

IEEE-488 PROGRAMMING
4.8.8 Serial Polling (SPE,SPD)
The serial polling sequence is used to obtain the Model
194 status byte. The status byte contains important infor-
mation about internal functions, as described in paragraph
4.9.16. The serial polling sequence can also be used by the
controller to determine which instrument on the bus has
asserted SRQ (Service Request).
The serial polling sequence is generally conducted as
follows:
1. The controller sets ATN true.
2. The controller then places the SPE (Serial Poll Enable)
command byte on the data bus. At this point, all active
devices are in the serial poll enabled mode and waiting
to be addressed.
3. The Model 194 is then addressed to talk.
4. The controller sets ATN f&c.
5. The instrument places its status byte on the data bus
to be read by the controller.
6. The controller then sets ATN true and places the SI'D
(Serial Poll Disable) command byte on the data bus to
end the serial polling sequence.
Once instruments are in the serial poll mode, steps 3
through 5 above can be repeated by sending the correct
talk address for each instrument.
HP-85 Programming Example-The HP-85 SPOLL state-
ment automatically performs the sequence just described.
To demonstrate serial polling, type in the following
statements:
When the above statements are executed, the Model 194
is serial polled, and the decimal value of the status byte
is displayed on the computer CRT.
Model 8573 Pmgmmming Example-Serial poll the Model
194 from the IBM PC computer as follows:
When the statements above are cxccutcd, the instrument
is serial polled and the decimal value of the status byte
is displayed on the computer CRT.
4.9 DEVICE-DEPENDENT COMMAND
PROGRAMMING
IEEE-488 device-dependent commands concerned with the
Model 194 are the most important comn~~mds associated
with the instrument because they control most instrument
operating modes. All front panel modes (such as rate and
samples), as well as some modes not .wail.lble from the
front panel (like SRQ and terminator) can bc progr~unmcd
with these commands.
Command Syntax
Each command is made up of a single ASCII capital letter
followed by one or more numbers representing rln option
or numeric parameter of that command. For example, the
range can be set over the bus by sending the letter "I?
followed by a number representing the range opt&l.
Some commands have two parameters that must tw
separated by commas. For example, a typical sampling iate
is programmed with the following comnund string:
SLl,lOOE-6X. The first parame&r in this case (0) is a con1-
mand option that instructs the instrument to program the
sampling rate in seconds, while the second parameter (l(x))
is the actual programming data. In this instance, a sampl-
ing rate of 100psec is being programmed.
NOTE
The following charac&rs may bc used in place of
a comma: ! @ # $ % f\ & ( ) = \ ; < > ? : ;
<space >
Those commands which require numeric data can be pn~
grammed in either floating point or scientific notation
Thus, the following sets of commands are equivalent:
Programmed
Floating Scientific
Mode
Point Notation
Buffer pointer
Bl,lOOX
Bl,lEZX
Delay
wo,1oooox WO,IE4X
4-15