Exercises

1. Rearrange the circuit in Figure 2.5 to convert the AND gate to a NAND gate. Hint: there is no need to add or remove components.
2. Create a circuit implementation of an OR gate by modifying the circuit in Figure 2.5. Wires, transistors, and resistors can be added as needed.
3. Search the internet for free VHDL development software suites that include a simulator. Get one of these suites, set it up, and build any simple demo projects that come with the suite to ensure it is working properly.
4. Using your VHDL tool set, implement the 4-bit adder using the code listings presented in this chapter.
5. Add test driver code (search the internet for VHDL testbench to find examples) to your 4-bit adder to drive it through a limited set of input sets and verify that the outputs are correct.
6. Expand the test driver code and verify that the 4-bit adder produces correct results for all possible combinations of inputs.

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