Campbell CR6 Series, Руководство оператора

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Section 7. Installation
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Q : What are the termination conditions that will stop incoming data from being
stored?
A : Termination conditions:
•
TerminationChar argument is received
• MaxNumChars
argument is met
• TimeOut argument is exceeded
SerialIn() does NOT stop storing when a Null character (&h00) is received
(unless a NULL character is specified as the termination character). As a string
variable, a NULL character received will terminate the string, but nevertheless
characters after a NULL character will continue to be received into the variable
space until one of the termination conditions is met. These characters can later
be accessed with MoveBytes() if necessary.
Q : How can a variable populated by SerialIn() be used in more than one
sequence and still avoid using the variable in other sequences when it contains old
data?
A : A simple caution is that the destination variable should not be used in more
than one sequence to avoid using the variable when it contains old data.
However, this is not always possible and the root problem can be handled more
elegantly.
When data arrives independent from execution of the CRBasic program, such as
occurs with streaming data, measures must be taken to ensure that the incoming
data are updated in time for subsequent processes using that data. When the task
of writing data is separate from the task of reading data, you should control the
flow of data with deliberate control features such as the use of flags or a
time-stamped weigh point as can be obtained from a data table.
There is nothing unique about SerialIn() with regard to understanding how to
correctly write to and read from global variables using multiple sequences.
SerialIn() is writing into an array of characters. Many other instructions write
into an array of values (characters, floats, or longs), such as Move() ,
MoveBytes() , GetVariables() , SerialInRecord() , SerialInBlock() . In all cases,
when writing to an array of values, it is important to understand what you are
reading, if you are reading it asynchronously, in other words reading it from some
other task that is polling for the data at the same time as it is being written,
whether that other task is some other machine reading the data, like LoggerNet , or
a different sequence, or task, within the same machine. If the process is
relatively fast, like the Move() instruction, and an asynchronous process is
reading the data, this can be even worse because the “reading old data” will
happen less often but is more insidious because it is so rare.
7.7.19 String Operations
String operations are performed using CRBasic string functions.