Interface Design

Rule #5:

Design smart Interfaces (Required)

• External Interfaces require a reduced set of parameter types (e.g. no POINTER).

  They should be optimized for the use with CFC.

  They should use the "Common Behavior Model"

• Internal interfaces can use the full set of parameter types.

We can distinguish between two types of interfaces

• External Interfaces –- Accessed by the end user application

• Internal Interfaces –- All other Interfaces!

For external interfaces we propose to use a reduced set of parameter types. With this, the end user has no need to use dangerous or compli­cated data types like POINTER or the ADR() operator. Interfaces should be optimized for the use with CFC. It is a good practice to reuse the "Common Behavior Model" to build function block interfaces for end users. Libraries, which are especially implemented regarding end user requirements, will be indicated by a special quality mark.

The following property:

marks libraries which are especially suitable for the usage by end users.

• Resource Management

• Asynchronous function blocks

• Synchronous functions with safe handles

• Usage of a "Common Behavior Model" (CBM)