Campbell Scientific CR7 Measurement and Control System - Manual (Page 16)

CR7 MEASUREMENT AND CONTROL SYSTEM OVERVIEW
OV-6
3. Final Storage - Final, processed values are
stored here for transfer to printer, solid state
Storage Module or for retrieval via
telecommunication links. Values are stored
in Final Storage only by the Output
Processing Instructions and only when the
Output Flag is set in the users program.
The 18,336 locations allocated to Final
Storage at power up is reduced if Input or
Intermediate Storage is increased.
4. System Memory - used for overhead tasks
such as compiling programs, transferring
data, etc. The user cannot access this
memory.
5. Program Memory - available for user
programs entered in Program Tables 1 and
2, and Subroutine Table 3. (Sections OV3,
1.1)
The use of the Input, Intermediate, and Final
Storage in the measurement and data
processing sequence is shown in Figure OV2-1.
While the total size of these three areas
remains constant, memory may be reallocated
between the areas to accommodate different
measurement and processing needs (*A Mode,
Section 1.5). The size of system and program
memory are fixed.
OV2.2 CR7 INSTRUCTION TYPES
Figure OV2.1 illustrates the use of the three
different instruction types which act on data.
The fourth type, Program Control, is used to
control output times and vary program
execution. Instructions are identified by
numbers.
1. INPUT/OUTPUT INSTRUCTIONS (1-
26,101-104, Section 9) control the terminal
strip inputs and outputs (the sensor is the
source, Figure OV1-2), storing the results in
Input Storage (destination). Multiplier and
offset parameters allow conversion of linear
signals into engineering units. The Control
Ports and Continuous Analog Outputs are
also addressed with I/O Instructions.
2. PROCESSING INSTRUCTIONS (30-66,
Section 10) perform numerical operations
on values located in Input Storage (source)
and store the results back in Input Storage
(destination). These instructions can be
used to develop high level algorithms to
process measurements prior to Output
Processing (Section 10).
3. OUTPUT PROCESSING INSTRUCTIONS
(69-82, Section 11) are the only
instructions which store data in Final
Storage (destination). Input Storage
(source) values are processed over time to
obtain averages, maxima, minima, etc.
There are two types of processing done by
Output Instructions: Intermediate and Final.
Intermediate processing normally takes
place each time the instruction is executed.
For example, when the Average Instruction
is executed, it adds the values from the
input locations being averaged to running
totals in Intermediate Storage. It also keeps
track of the number of samples.
Final processing occurs only when the
Output Flag is high. The Output Processing
Instructions check the Output Flag. If the
flag is high, final values are calculated and
output. With the Average, accumulated
totals are divided by the number of samples
and the resulting averages sent to Final
Storage. Intermediate locations are zeroed
and the process starts over. The Output
Flag, Flag 0, is set high by a Program
Control Instruction which must precede the
Output Processing Instructions in the user
entered program.
4. PROGRAM CONTROL INSTRUCTIONS
(85-98, Section 12) are used for logic
decisions and conditional statements. They
can set flags, compare values or times,
execute loops, call subroutines,
conditionally execute portions of the
program, etc.
OV2.3 PROGRAM TABLES AND THE
EXECUTION AND OUTPUT INTERVALS
Programs are entered in Tables 1 and 2.
Subroutines, called from Tables 1 and 2, are
entered in Subroutine Table 3. The size of each
table is flexible, limited only by the total amount
of program memory. If Table 1 is the only table
programmed, the entire program memory is
available for Table 1.
Table 1 and Table 2 have independent
execution intervals, entered in units of seconds
with an allowable range of 0.0125 to 6553
seconds. Intervals shorter than 0.1 seconds are
allowed only in Table 1. Subroutine Table 3 has
no execution interval; subroutines are only
executed when called from Table 1 or 2.