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The
SECTION
3.
INSTRUCTION SET BASICS
used
to
program
the
21X are divided into 4 types: lnput/Output (l/O), Processing,
Output
and Program
Control. l/O
lnstructions
are used
to
make measurements
and
store the
in input locations or to initiate analog or digital pott
output.
Processing
lnstructions
numerical operations using data from
lnput Storage locations and place the
method for gjenerating time or event dependent data summaries from
processed sensor readings
residing in
sfiecified lnput Storage
locations. Program
Control lnstructions
are used to direct
program
ex*ution
based
on time and/or conditional
tests
on input data and to direct
output
to
erternaldedces.
lnstructions
Are
identified by a
number.
Each
instruction
has
a number
of
parameters which give
the
21X the lnformation it needs to execute the instruction.
l
The
set
of
inbtructions available
in
the
2lX
is determined
by the Programmable Read Only
Memory chifis (PROMS) that are installed. Appendix
B
lists
the software options available.
3.1
PARAMETER DATA TYPES
There are
3
flifferent data types used for
Instruction
pprameters: Floating Point (FP),
4
digit integer{ (4), and 2 digit integers
(2).
In
the
listings
of
th$ instruction parameters (Sections
9-12),
the
data
type is identified by
its
allow the
21
Different data types
are used to
to make the most efficient use of
its memory.
Floating Point parameters are used to enter
numeric conbtants for
calibrations or arithmetic
operations.
[A/hile
it
is
only possible
to enter
5
digits (magnftude
t.00001 to t99999.),
the
internalfornlat
has
a much greater range
(1x10-ts
to
Qx1018,
Section 2.2.1).
3.2
REPETITIONS
The repetitiqns parameter on many of the l/O,
Processing, and
Output Processing lnstructions
is used
to repeat the instruction on a number of
sequential lflput Channels or lnput Storage
locations.
For
example,
if
you have 4 ditferential
voltage meapurements
to
make on
the same
voltage rangp, wire the inputs to sequential
channels anp instead of entering
the Ditferential
Voltage
Me{surement Instruction 4 times, enter
it
once
with
fr
repetitions. The instruction will
make
4 me{surements starting on the specified
channel number and continuing through the
3
succeeding pifferential channels, with
the results
being
store(
in
the
specified input location and
the
3
succe$ding input locations. Averages for
all
4 measuiements can be calculated by
entering the
Average Instruction with
4
repetitions-
When several of the same type of
measurements are
to be made but the
calibrations
of
the sensors are different,
it
requires less time
to use a single measurement
instruction
with repetitions and then apply the
calibrations
with Instruction 53 than
it
does
to
enter
the instruction several times in order to
use
different multipliers and
offsets. This
is due
to
the set up and calibration time for each
measurement
instruction.
However,
if
time
is
not a
constraint, separate instructions may make
the program easier to follow.
3.3
ENTERING NEGATIVE NUMBERS
After keying in a number, press C or
"-"
to
change
the number's
sign.
On
floating point
numbers a minus sign
O
will appear to the left
of
the number.
Excitation
voltages in millivolts for l/O
Instructions are 4
digit integers;when C
is
pressed, minus signs
(-)
will appear to the right
of
the number indicating a negative excitation.
Even though this
display
is
the same as that
indicating
an indexed input location, (Section
3.4)
there is no indexing effect on excitation
voltage.
3.4
INDEXING INPUT LOCATIONS
When used within a Loop, the parameters for
input locations
can be Indexed to the loop
3-1
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