The required sizes for these parameters depend on the application. The generic parameter digits in the ENTITY sets the width of the bcd output port, defining the range of BCD numbers the converter outputs. The generic parameter bits in the ENTITY sets the width of the binary input port, defining the range of binary numbers the converter accepts. Multi-Digit Binary to BCD Converter Setting the Binary Number Size and the Number of BCD Digits Binary to BCD Shift Register Truth Tableįigure 3. In this case, a 1 is shifted into the next larger BCD digit’s register, and the current digit’s register is adjusted to contain the appropriate value. So, if the current number is greater than 4, it cannot be doubled merely by shifting the bits. Since the maximum value each 4-bit BCD digit can have is 9, the component needs to make an adjustment if the doubling process results in a number greater than 9. Once the entire number is shifted in, the new BCD number is equivalent to the original binary one. With each shift, it doubles the register’s current value and adds the new bit. This component completes the same process to perform a Binary to BCD conversion. Once you have shifted in all of the bits, the new register contains the original number. Each time you shift in a bit, you are doubling the current number in the register and adding the new bit. Suppose you shift a number from one binary register into another binary register, one bit at a time. The concept behind this Binary to BCD converter is to shift the number from one shift register into another shift register, most significant bit (MSB) first. Example Implementation Theory of Operation An example design that uses this Binary to BCD Converter to make a Multiple Digit 7-Segment Display Driver is available here.įigure 1. Figure 1 illustrates a typical example of the Binary to BCD converter integrated into a system. Resource requirements depend on the implementation. It was designed using Quartus II, version 13.1.0. The component reads in a binary number from user logic over a parallel interface and outputs the BCD equivalent. This details a Binary to BCD converter circuit, written in VHDL for use in CPLDs and FPGAs. Configurable number of BCD output digits.Configurable size of binary input number. VHDL source code of a Binary to Binary Coded Decimal (BCD) converter component.Outputs F3 to F0 will have valid values only when E=0, else they will be zero.ĭecoders can be used in various digital circuits, such as address decoding in memory and input/output devices, data conversion, and data encryption.Binary to BCD Converter (top-level VHDL for the design): binary_to_bcd.vhd (5.8 KB)īinary to BCD Digit Converter (must be included in project): binary_to_bcd_digit.vhd (3.2 KB) Features Thus, the output F1 will be 1 (HIGH voltage level) and all other outputs (F3, F2 and F0) will be 0 (LOW voltage level).Īn enable (E) pin can be added to the circuit to disable the decoder. The output line corresponding to the binary code of the inputs will have a HIGH voltage level or logic 1, while all other output lines will have a LOW voltage level or logic 0.įor example, if A=0 and B=1, the binary code applied to the decoder is 01, which corresponds to output line F1. The binary input code applied to the two input lines A and B selects one of these four output lines. In this circuit, there are two input lines A, B, and four output lines F3 to F0. The implementation of a 2-to-4 line decoder with enable is shown below: The implementation of a decoder depends on the number of input and output lines. The decoder enables only one output at a time for a specific combination of input bits. The binary decoder has N input lines (A0 to An-1) and 2 N output lines (Y0 to Y2 N-1). The most commonly used decoder is the binary decoder, which converts a binary input code into a set of outputs. The decoder takes the binary code on its N input lines and activates the output line corresponding to the binary code. It has N input lines and 2 N output lines. A decoder is a combinational circuit that converts a binary code into a set of output signals.
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