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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

The Program Counter

A Fetch-Decode-Execute Cycle Map

The Program Counter (or PC) is a register inside the microprocessor that stores the memory address of the next instruction to be executed. In ARM processors, the Program Counter is a 32-bit register which is also known as R15.

The processor first fetches the instruction from the address stored in the PC. The fetched instruction is then decoded so that it can be interpreted by the microprocessor. Once decoded, the instruction can then be executed and the PC incremented so that it contains the address of the next instruction. This is known as the fetch-decode-execute cycle.

In ARM processors, all instructions take up one word (4 bytes). Hence incrementing the PC actually adds 4 to its value as memory addresses are given in bytes but aligned on word boundaries.