Tools

Combinational Logic Design            

Assignment Statements for Ripple Carry Adder:

  • Create a half adder circuit using only logic gates and test it by giving proper input.
  • Create a full adder circuit using only logic gates and test it by giving proper input.
  • Create a full adder circuit using half adder and test it by giving proper input.
  • Create a 4-bit ripple carry adder circuit using half adders and full adders and test it by giving proper input.

Circuit diagram of Ripple Carry Adder:

Procedure

  • To draw any diagram in the simulator please follow the manual given in manual section.
  1. Half Adder with ‘XOR’ and ‘AND’ gates readily available in the simulator.
where

20, 21: Input bits

26: Sum

27: Carry

  • This could be saved as a component with suitable name – say ‘HalfAdder’.
  1. Full Adder with ‘XOR’, ‘AND’ and ‘OR’ gates readily available in the simulator.

where

82, 83: Input Bits

84: Carry-In

85: Sum

87: Carry-Out

  1. Full Adder with the help of Half Adders (Designed Above) and ‘OR’ gate
where

1, 15: Half Adders

62, 63: Input Bits

64: Carry-In

65: Sum

66: Carry Out

  • This could be saved as a component with suitable name – say ‘FullAdder’.
  1. Ripple Carry Adder with 1 half adder and 3 full adders
  • 1: Half Adder and 15, 52, 89: Full Adder
  • First 4 bit number represented by 183(LSB), 185, 187 and 189(MSB) and second 4 bit number represented by 184 (LSB), 186, 188, 190 (MSB).
  • The output number after sum is 191 (LSB), 192, 193, 194 (MSB).
  • Final carry-out is 195.

Assignment Statements for Carry-Lookahead Adder:

  • Create a full adder circuit using basic logic gates and test it by giving proper input.
  • Create a Pi-Gi generator circuit using basic logic gates and test it by giving proper input.
  • Create 3 input AND gate, 3 input OR gate, 4 input AND gate, 4 input OR gates using basic logic gates and test it by giving proper input.
  • Create a carry generator using above GATEs and test it with proper input
  • Create a 4-bit carry lookahead adder circuit using Pi-Gi generator, carry generator and Full Adders.

Procedure

To draw any diagram in the simulator, please follow the instructions given in the manual.

  1. Create a Pi-Gi generator as shown below. For Pi-Gi, please refer to the theory section. Save this as a component, say pi-gi.

Pi-Gi generator

where

24: Ai,   25: Bi   26: Pi   27: Gi

  1. Create carry generator as shown in the picture below using basic AND gate, basic OR gate, 3 input AND, 3 input OR, 4 input AND, 4 input OR gates and save it as a component say c-gen.

Carry Generator for 4 bit carry-lookahead adder

where

210: C1,   211: G1,   212: P1,   213: G2,   214: P2,   215: G3,   216: P3,   217: C2,   218: C3,   219: C4

  1. Create a 4 bit carry lookahead adder as shown below using Pi-Gi generator, c-gen and 1 bit Full Adder.

4-bit carry-lookahead adder

395: Cin,   387: A1,   388: B1,   389: A2,   390: B2,   391: A3,   392: B3,   393: A4,   394: B4,   396: S1,   397: S2,   398: S3,   399: S4  

448: S5 [A1, B1: LSB A4, B4: MSB S1: LSB, S5: MSB]

Follow the below manual and perform the experiment