The ALU for the 8 bit computer.

Notes

• The Diagram
• Parts
  • 74x245 - tri-state device to control data to the bus
  • 74x283 - 4 bit adder
    • 4 A inputs
    • 4 B inputs
    • A carry in
    • 4 sum outputs
    • 1 carry out output
  • 74x86 - xor gate
    • 4 a inputs
    • 4 b inputs
    • 4 a ⊕ b outputs
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    b	su	b⊕su
    0	0	0
    0	1	1
    1	0	1
    1	1	0

  • If su is 0, the b bit is preserved
  • If su is 1, the b bit is flipped
• Building the Circuit
  • He has an input of A and B (wired directly to the registers.
  • He has an input of su, which he runs through the xor gates with the values from b.
  • He wires the outputs of b ⊕ su to the b inputs of the adders
  • He wires a to the inputs of the adders.
  • He wires the outputs of the adders to the tristate
  • 
  • 
  • The Digital File
• There is also a flags register located on this breadboard
  • It includes the carry_out from the second adder
  • And a circuit to compute the zero of the addition.