GE PACSystems RX7i Cpu Programmer's Reference Manual page 387

Chapter 8. Structured Text (ST) Programming
Formal Calls vs. Informal Calls
PACSystems supports formal and informal calls in ST.
Formal Calls
Input parameter assignments use the ':='
notation while output assignments use the '=>'
notation.
Optional parameters can be omitted.
Parameters can be in any order.
The ENO parameter is specified in a formal
function or block call.
All built-in functions and user-defined blocks
have an optional ENO output parameter
indicating the success of the function or block.
Either ENO or Y0 can be used as this output
parameter name.
Format of Formal Function Call
FunctionName(IN1 := inparam1, IN2 := inparam2, OUT1 => outparam1, ENO => enoparam);
Format of Informal Function Call
FunctionName(inparam1, inparam2, outparam1);
Example
This code fragment shows the TAN function call.
TAN( AnyReal, Result );
372 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual
Informal Calls
Input and output parameters are listed in parentheses.
Parameters cannot be omitted.
Parameters must be in the correct order as follows:
Inputs
Instance location (if required)
Length parameter (if required)
Outputs, starting with the last output
parameter.
The ENO parameter is not specified in an informal
function or block call.
GFK-2950C