Omron CX-PROGRAMMER V8.1 Operation Manual page 24

Application Precautions
an input-output variable specified as an array variable (with the first
address set for the input parameter) and specify the first or last element of
the array variable, or, with any version of CX-Programmer, use an internal
variable with an AT setting. Alternatively, specify the first or last element in
an internal variable specified as an array variable.
• Values are passed in a batch from the input parameters to the input vari-
ables or input-output variables before algorithm execution (not at the
same time as the instructions in the algorithm are executed). Therefore, to
pass the value from a parameter to an input variable or input-output vari-
able when an instruction in the function block algorithm is executed, use
an internal variable or external variable instead of an input variable or
input-output variable. The same applies to the timing for writing values to
the parameters from output variables.
• Always use internal variables with AT settings in the following cases.
• The addresses allocated to Basic I/O Units, Special I/O Units, and
CPU Bus Units cannot be registered to global symbols, and these vari-
ables cannot be specified as external variables (e.g., the data set for
global variables may not be stable).
• Use internal variables when Auxiliary Area bits other than those pre-
registered to external variables are registered to global symbols and
these variables are not specified as external variables.
• Use internal variables when specifying PLC addresses for another
node on the network: For example, the first destination word at the re-
mote node for SEND(090) and the first source word at the remote node
for RECV(098).
• Use internal variables when the first or last of multiple words is speci-
fied by an instruction operand and the operand cannot be specified as
an array variable (e.g., the number of array elements cannot be spec-
ified).
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