Introduction to Digital Systems: Modeling, Synthesis, and Simulation Using VHDL

7.8 CODE CONVERTERS

Decoder and encoder circuits are used to convert from one type of input encoding to a different output encoding. For example, a 2: 4 decoder converts a 2-bit binary number input to a one-hot encoding sequence (see Section 9.6) at the output. Similarly, a 4: 2 binary encoder performs the opposite conversion. There are many other possible types of code converters known as BCD-to-seven-segment code converter, BCD-to-Gray code converter, BCD-to-excess-3 code converters, and so on.

Figure 7.21 4 : 2 Binary Encoder

Figure 7.22 4: 2 Priority Encoder

7.8.1 BCD-to-Seven-Segment Code Converter

A BCD-to-seven-segment code converter converts one binary-coded decimal (BCD) digit into information suitable for driving a digit-oriented display such as a seven-segment display. In other words, it converts the BCD digit into seven signals that are used to drive the segments in the display. The circuit of the BCD-to-seven-segment code converter has four binary inputs (x₁, x₂, x₃, and x₄), representing the BCD number, and seven binary outputs (a, b, c, d, e, f, and g) representing the LED segments. Each segment is a small LED, which glows when driven by an electrical signal. The BCD-to-segment code conversion truth table and a seven-segment LED display are shown in Figure 7.23. The ...