Understanding the CPU and Memory Interaction

Overview of the CPU

• CPU (Central Processing Unit) Functions:
  • Executes programs or code.
  • Reads data from external memory byte by byte.
• Memory Structure:
  • Organized as an array of integers called bytes (0-255).
  • Memory cells are numbered starting from zero (addresses).

Types of Memory

• Read-Only Memory (ROM):
  • Contains pre-programmed code (firmware).
  • Only read by the CPU.
  • Data remains even when power is off.
• Random Access Memory (RAM):
  • Contains temporary data, loaded by the CPU.
  • Can be read and written to by the CPU.
  • Data is lost when power is off.

Memory Addressing and Communication

• Address Bus:
  • Communication system for the CPU to tell memory which cell to access.
  • Uses binary system to encode memory cell addresses.
  • CPU uses binary values to communicate addresses.
• Control Bus:
  • Signaling system for memory operations (Read/Write).
  • CPU pulls lines low to activate signals (active low).
  • Read and Write lines are mutually exclusive.
• Data Bus:
  • Transfers data between CPU and memory.
  • Bi-directional, can carry data to/from CPU.

Address Decoding

• Address range allocation in memory:
  • Address space divided into fixed ranges for ROM and RAM.
  • Example: CPU with 16 address lines can access 64KB memory.
  • ROM takes lower range, RAM takes upper range for initialization.

Interaction of CPU with Memory

• ROM and RAM Communication:
  • CPU starts reading code as soon as power is applied.
  • Uses Read line to read memory and Write line to write memory.
  • Address bus ensures that ROM/RAM are addressed correctly during access.
• Hexadecimal Representation:
  • Used to simplify binary data representation.
  • Memory and addresses often represented in hex for ease.

Adding More Modules to a Simple Computer

• Input/Output Ports:
  • Allows user interaction (keyboard, mouse, gamepad).
  • Decoded into separate address space and accessed with special instructions.
• Example of LED Control:
  • CPU can use machine code instructions to control ports like turning an LED on/off.
  • Uses specific address and data bus for the interactions.

Conclusion

• The lecture provides a comprehensive overview of CPU functions, memory types and communication, and basic principles of address decoding and hardware interactions.
• Key takeaway: The interaction between the CPU, memory, and peripherals hinges upon precise addressing and decoding mechanisms.