Lecture 10 Circuit Basics of Microprocessor

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Lecture 10Circuit Basics of Microprocessor
Youpyo Hong _at_ DGU
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Unused Inputs

• Do not forget to connect unused inputs to High or
  Low.
• Pull-up or Pull-down is a widely used connection.

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Transistor Basics

• A digital IC basically consists of gates.
• A gate consists of transistors.

Gate
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P-transistor and N-transistor
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Drain and Source of a Transistor
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Connecting Multiple Outputs

• (x)

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Open Drain Terminal for MOS

• If at least one input is high, output is stable
  low.
• If two inputs are low, two transistors are off.
  Then the output is floating.

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Pull-Up for Open-Drain Terminal

• If at least one input is high, output is still
  stable low.
• If two inputs are low, output is stable high.

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Open Collector Terminal for Bipolar
output
output
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Open Drain or Open Collector

• Used to connect multiple terminals directly
  without using tri-state terminal or multiplexor.
• Make sure to place pull-up resistors.

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Pull-up or Pull-down Resistors

• When you connect unused inputs to 0 or 1, it is
  recommended to use resistors between the inputs
  and power-supply (or Ground.)
• Why? To avoid damaging the chip due to too much
  current flow.