Operator`s manual

3-1
SECTION 3. INSTRUCTION SET BASICS
The instructions used to program the 21X are divided into 4 types: Input/Output (I/O), Processing,
Output Processing, and Program Control. I/O Instructions are used to make measurements and
store the readings in input locations or to initiate analog or digital port output. Processing
Instructions perform numerical operations using data from Input Storage locations and place the
results back into specified Input Storage locations. Output Processing Instructions provide a
method for generating time or event dependent data summaries from processed sensor readings
residing in specified Input Storage locations. Program Control Instructions are used to direct
program execution based on time and/or conditional tests on input data and to direct output to
external devices.
Instructions are identified by a number. Each instruction has a number of parameters which give
the 21X the information it needs to execute the instruction.
The set of instructions available in the 21X is determined by the Programmable Read Only
Memory chips (PROMS) that are installed. Appendix B lists the software options available.
3.1 PARAMETER DATA TYPES
There are 3 different data types used for
Instruction parameters: Floating Point (FP), 4
digit integers (4), and 2 digit integers (2). In the
listings of the instruction parameters (Sections
9-12), the parameter data type is identified by its
abbreviation. Different data types are used to
allow the 21X to make the most efficient use of
its memory.
Floating Point parameters are used to enter
numeric constants for calibrations or arithmetic
operations. While it is only possible to enter 5
digits (magnitude ±.00001 to ±99999.), the
internal format has a much greater range
(1x10
-19
to 9x10
18
, Section 2.2.1).
3.2 REPETITIONS
The repetitions parameter on many of the I/O,
Processing, and Output Processing Instructions
is used to repeat the instruction on a number of
sequential Input Channels or Input Storage
locations. For example, if you have 4 differential
voltage measurements to make on the same
voltage range, wire the inputs to sequential
channels and instead of entering the Differential
Voltage Measurement Instruction 4 times, enter
it once with 4 repetitions. The instruction will
make 4 measurements starting on the specified
channel number and continuing through the 3
succeeding differential channels, with the results
being stored in the specified input location and
the 3 succeeding input locations. Averages for
all 4 measurements 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 (-) will appear to the left
of the number.
Excitation voltages in millivolts for I/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