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Operation
Model 8902A
"Instrument Preset" in the Detailed Operating Instrirctions on page 3-239 for a description of the intial
instrument condtions.) The
made to conform with the
block in the supervisor is where the hardware state is
The. hardware state is the actual, current state of the internal settings of the instrument and is only
updated when enough time is allowed between commands for the Software Supervisor measurement
loop to be completed successfully without interruption; e.g., when a trigger is received.
and
1 - 1
blocks manipulate hardware as well and also
to make an accurate measurement.
A measurement is not
made
until all blocks are successfully completed in succession. If a block
is
not completed, a negative
decision after that block then forces the program back to the top of the supervisor, bypassing
for that loop.
In a normal, stable measurement cycle, the program takes the
[Measurement Dlsplayl
branch at the top
of the supervisor and so avoids the extra time associated with the
1 - 1
block. However,
if the program loops back before taking a measurement, o r if an error condition exists, the
INon-Measurement Dlsplay]
branch will be traversed. This will light an appropriate display, which is usually
1'-
- -
",
and send the program back through the
1 - 1
block.
After power-up, the external system controller can be thought
of
as a medium through which the user
requests a certain instrument setup which is first implemented in software state and then in hardware
state. Controller commands
(
Keyboard or HP-IB interrupts]
)
are treated as non-returnable interrupts and
break the flow around the
So
are Supervisor loop, forcing the internal microprocessor
to
execute
a short program to change the software state and then return
to the
loop as shown in the diagram.
The commands applicable to the measurement mode are implemented in software state and then in
hardware state at the next
7
1
.
NOTE
Controller roirfines modfy only the sojlware state and do not
a@ct
the
hardware immedia tcly.
Since a
IKeyboard or HP-IB interrupt]
can infcw'irpf the Sirptv'visor af any point
and retirrn it
to
the point in the loop before
- 1 ,
these inft'rnipts
abort thc cirrrcnf mt'asiircmcnt and start a new measiirc~ment cycle.
The adiral insfriimenf sdirp is guarankw/
lo
confbrm
f o
fhe Keyboard
ri~qi~iW
only at the rnomcnl a mcaasirrcmcnl is lakcw
(
F l ) .
3-36
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