Campbell Scientific PC400 Datalogger Support Software - Manual (Page 190)

Section 9. Datalogger Program Creation with CRBasic Editor
TABLE 9-3. Synonyms for True and False
Predefined Constant True (-1) False (0)
Synonym High Low
Synonym On Off
Synonym Yes No
Synonym Trigger Do Not Trigger
Number ≠0 0
Digital port 5 Volts 0 Volts
9
9
.4.11.2 Expression Evaluation
Conditional tests require the datalogger to evaluate an expression and take one
path if the expression is true and another if the expression is false. For
example:
If X>=5 then Y=0
will set the variable Y to 0 if X is greater than or equal to 5.
The datalogger will also evaluate multiple expressions linked with and or or.
For example:
If X>=5 and Z=2 then Y=0
will set Y=0 only if both X>=5 and Z=2 are true.
If X>=5 or Z=2 then Y=0
will set Y=0 if either X>=5 or Z=2 is true (see And and Or in the help). A
condition can include multiple and and or links.
.4.11.3 Numeric Results of Expression Evaluation
The datalogger’s expression evaluator evaluates an expression and returns a
number. A conditional statement uses the number to decide which way to
branch. The conditional statement is false if the number is 0 and true if the
number is not 0. For example:
If 6 then Y=0,
is always true, Y will be set to 0 any time the conditional statement is executed.
If 0 then Y=0
is always false, Y will never be set to 0 by this conditional statement.
The expression evaluator evaluates the expression, X>=5, and returns -1, if the
expression is true, and 0, if the expression is false.
W=(X>Y)
will set W equal to -1 if X>Y or will set W equal to 0 if X<=Y.
The datalogger uses -1 rather than some other non-zero number because the
and and or operators are the same for logical statements and binary bitwise
comparisons. The number -1 is expressed in binary with all bits equal to 1, the
number 0 has all bits equal to 0. When -1 is anded with any other number the
result is the other number, ensuring that if the other number is non-zero (true),
the result will be non-zero.
9-28