Question 1 a. Tri-state logic is often used in digital design to resolve the conflict that arises when more than one output is connected. With the aid of a diagram, explain how this can be used in a digital design to share a single bus. b. Examine the following VHDL statements and draw a synthesised schematic for the corresponding design. c. Using concurrent statements only, (no process), describe a decoder in VHDL which satisfies the following conditions, and draw the High level RTL schematic for this design. 3 inputs (A, B, C) and 1 output (Z). The output is equal to 1 when either input A is equal to 1 or only input C is equal to 1. All signals are of type 'std_logic
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Question 1 a. Tri-state logic is often used in digital design to resolve the conflict that arises when more than one output is connected. With the aid of a diagram, explain how this can be used in a digital design to share a single bus. b. Examine the following VHDL statements and draw a synthesised schematic for the corresponding design. c. Using concurrent statements only, (no process), describe a decoder in VHDL which satisfies the following conditions, and draw the High level RTL schematic for this design. 3 inputs (A, B, C) and 1 output (Z). The output is equal to 1 when either input A is equal to 1 or only input C is equal to 1. All signals are of type 'std_logic d. VHDL allows the designer to describe hardware using different language constructs. Although, these constructs might have the same, or similar, functionality, the result of the synthesis is quite different. One example is the if-else and the case constructs. Explain the difference between the if-else and the case construct with respect to simulation and synthesis. entity EXAMPLE IS PORT ( P, Q, R : IN STD_LOGIC; PQ : OUT STD_LOGIC; PQR : OUT STD_LOGIC); end EXAMPLE; architecture RTL of EXAMPLE is signal PQ_SIG: std_logic; begin PQ_SIG <= P and Q; PQR <= PQ_SIG and R; PQ <= PQ_SIG; end RTL; Question 2 a. The VHDL language can use concurrent statements as well as sequential statements. Explain the difference between these two statements. b. Verification of the final ASIC is an important stage in the ASIC design process. Latches can be difficult to test at this stage. It is, therefore, important to avoid any unnecessary latches in the synthesised design. Explain how a latch can be inferred. Give a VHDL code as an example. c. Following is the entity declaration for a simple serial in parallel out (SIPO) 8 bit shift register. Write a VHDL architecture for this entity so the data can be shifted to the left (LSB first) and right (MSB first). d. Write a VHDL description for the following digital circuit. Use a synchronous, active high reset
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