Due to this fact and due to the fact that an IEEE standard has to be revised every five years the new standard IEEE 1076-1993 was defined in the middle of 1993. The new hardware description language VHDL has found world-wide acceptability and has a lot of supporters. The traditional method of electronic design is bottom-up. Each design is performed at the gate-level using the standard gates. With increasing complexity of new designs this approach is nearly impossible to maintain.
New systems consist of ASICs or microprocessors with a complexity of thousands of transistors.
These traditional bottom-up designs have to give way to new structural, hierarchical design methods. Without these new design practices it would be impossible to handle the new complexity. A real top-down design allows early testing, easy change of different technologies, a structured system design and offers many other advantages. But it is very difficult to follow a pure top-down design. Figure 1 shows a Top-Down design approach.