Design an 8-4-2-1 BCD code converter to drive a seven-segment indicator. The four inputs to the converter circuit (A, B, C, and D in the figure above) represent an 8-4-2-1 binary-coded-decimal digit. Assume that only input combinations representing the digits 0 through 9 can occur as inputs so that the combinations 1010 through 1111 are don't-cares. Design your circuit using only two-, three-, and four-input NAND gates and inverters. Try to minimize the number of gates required. The variables A, B, C, and D will be available from toggle switches.
- Derive a truth table for the assigned problem.
- Use Karnaugh maps to derive logic equations in sum-of-products or product-of-sums form depending on whether NAND gates or NOR gates are required.
- Draw a circuit of AND and OR gates, trying to minimize the number of gates required by using common gates as appropriate. Factoring or multiplying out is required in some cases.
- Convert to NAND or NOR gates as specified.