Campbell Scientific CR7 Measurement and Control System - Manual (Page 43)

3-1
SECTION 3. INSTRUCTION SET BASICS
The instructions used to program the CR7 are divided into four 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
CR7 the information it needs to execute the instruction.
The set of instructions available in the CR7 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 three 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 CR7 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 five
digits (magnitude ±.00001 to ±99999.), the
internal format has a much greater range
(1x10-19 to 9x1018, Section 2.2.1).
3.2 REPETITIONS/CARD NUMBER
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. Separate parameters are used to
specify the card and input channel on which to
make the first measurement. For example, if
you have four 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 four repetitions. The instruction will make
four measurements starting on the specified
channel number and continuing through the
three succeeding differential channels, with the
results being stored in the specified input
location and the three succeeding input
locations. Averages for all four measurements
can be calculated by entering the Average
Instruction with four repetitions.
The CR7 will automatically continue repetitions
from the last channel of one card to the first
channel of the next sequentially numbered
723(-T) Analog Input Card or 725 Pulse Counter
Card. Measurements on the 726 50 volt Analog
Input Card will not advance correctly from one
card to the next; enter separate measurement
instructions for each card.
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.