CNC data interfaces

It is not surprising that CNC Data interfacing is a source of confusion in many plants. The many names by which CNC data interfaces are specified have been a contributing factor. Some of the more common terms are: data port, serial port, communications interface, behind-the-tape-reader interface (BTRI), DNC interface, and parallel port, to name a few. These terms are often combined with vague definitions and written into equipment specifications. For example, the following definitions are taken from actual specifications: * "A serial data port is required for future connection into a DNC or FMS system." * "A serial or parallel data port is required. A BTRI is acceptable." * "The control must have MAP communications compatibility." * "An RS-232 interface is required." * "A DNC interface is required."
The ambiguity of the above statements allows the CNC vendor to comply without defining what capability will be provided. For example, an RS-232 interface can include a very sophisticated protocol that provides error checking and status reporting capability, or it may not have any of these capabilities.
One way to minimize confusion is to use the International Standards Organization (ISO) seven-layer network architecture for local area networks (LANs). Even though this architecture is a model for open systems interconnection (OSI) for LANs, it can also provide a common base of understanding for serial interfaces as well. The seven layers consist of: (1) physical, (2) data link, (3) network, (4) transport, (5) session, (6) presentation and (7) application.