GE PACSystems RXi User Manual page 122

Using Parameters With an External Block
An external block may be defined to have between zero and 63 formal input parameters and
between one and 64 formal output parameters. A 'power-flow out' (or OK) parameter, named
Y0, is automatically defined for every external block. Y0 is a BOOL parameter of LENGTH 1,
and indicates the successful execution of the block. It can be read and written to by the
external block's logic.
The following table gives the TYPEs, LENGTHs, and parameter-passing mechanisms
allowed for external block parameters.
BOOL
BYTE
INT, UINT, and WORD
DINT, REAL, and
DWORD
LREAL
5
UDT
The PACSystems default parameter passing mechanisms correspond to the way that
external block parameters are passed on 90-70 controllers. The parameter passing
mechanisms of formal parameters cannot be changed from their default values.
You must define a name for each formal input and output parameter.
Arguments, or actual parameters, are passed into an external block when an external block
call is executed.
Arguments may be any valid reference address including an indirect reference, may be flow,
or may be a constant if the corresponding parameter's LENGTH is 1.
5
To use a UDT, you must include the UDT definition as a C structure in the external block. For details,
refer to Using a UDT as a C block input parameter data type in the online help.
GFK-2816F
Type Length
1 to 256
1 to 1024
1 to 512
1 to 256
1 to 128
1 to 128
Default Parameter Passing Mechanism
INPUTS: by reference
OUTPUTS: by reference; except Y0, which is
by initial-value result
INPUTS: by reference
OUTPUTS: by reference
INPUTS: by reference
OUTPUTS: by reference
INPUTS: by reference
OUTPUTS: by reference
INPUTS: by reference
OUTPUTS: by reference
INPUTS: by reference
OUTPUTS: not allowed
August 2015
Chapter 6. Program Organization
109