The maximum number of BCD digits required to represent a specific number of binary bits is defined by equation 1. In the first case, the user knows the size of his binary input numbers and needs to determine the appropriate number of BCD digits to represent his input range. There are two common scenarios for sizing these parameters: (1) calculate the BCD digits needed to represent a desired range of binary numbers, or (2) calculate the binary input size required to drive a desired number of BCD digits. 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.
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