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• 1. Microprocessor and Memory Basics
• What is a microprocessor and where are they used?
• Abstract system architecture
• System communication
  • Data bus, address bus, control bus
  • Reading data from memory
  • Writing data to memory
  • The Address Capacity of Memory
• Inside the microprocessor
  • The Arithmetic and Logic Unit
  • The Program Counter
  • Registers
• Inside memory
  • Memory Read and Write Operations
  • Calculating storage space
  • Address decoders
  • Tri-state buffers
  • Multiple memory chips
  • Other types of memory
  • Memory mapped input/output

Address Decoder

The animation below shows a "one out of 2ⁿ decoder" where n = 2. Only one output is high at any given time.

The word select lines are driven from the "one out of 2ⁿ decoder". Thus only one word select line is driven high at any time.

Word selection

The diagram below shows how the internal signals data in, data out, and write enable are connected to the external data bus wires, the read/write wire and chip select.

Connections of internal signals to external wires

If address decoding was performed by a single decoder, it would be a massive block of circuitry. Instead most architectures use a hierarchy of decoders to break the problem down into more manageable pieces. Usually the last stage of decoding (e.g. determining which of the 2²⁰ locations on the chip is required) is performed inside the memory chip itself.