Electrical realities

• ICs draw lots of current when switching

  • Power supply is typically far away
    • Many nanoseconds of wire
  • The chip supply voltage will drop
    • Degrading the outputs

• Add decoupling

  • A capacitor from Vdd to Gnd
    • Right at the chip pins
  • Keeps voltage from dropping
    • I = CdV/dt

• Tie unused chip inputs to gnd

  • Prevents random switching

From Motorola HC data book

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