The document discusses the control unit (CU) of a computer's central processing unit (CPU). It explains that the CU controls instruction execution sequence, interprets instructions, guides data flow, regulates timing, and handles tasks like fetching, decoding, and storing results. The CU has three main components: sequential logic, control unit registers and decoders, and control memory where microprograms are stored. The document also compares hardwired control units, which have fixed circuitry, to microprogram control units, which use replaceable microprograms stored in control memory.
4. Structure - The CPU
Computer Arithmetic
and
Login Unit
Control
Unit
Internal CPU
Interconnection
Registers
CPU
I/O
Memory
System
Bus
CPU
5. CU - Function
Controls sequential instruction execution
Interprets instructions
Guides data flow through different computer areas
Regulates and controls processor timing
Sends and receives control signals from other
computer devices
Handles multiple tasks, such as fetching, decoding,
execution handling and storing results
6. Structure - The Control Unit
CPU
Control
Memory
Control Unit
Registers and
Decoders
Sequencing
Logic
Control
Unit
ALU
Registers
Internal
Bus
Control Unit
7. CU - Component
Sequential logic : a type of logic circuit whose output
depends not only on the present value of its input signals
but on the past history of its inputs
Control Unit Registers and Decoders : register where to
place and translate instructions that can be understood by
the CPU
Control Memory : component where programs or
microprograms, that can move the sequencing process
laying and translation of instructions, are placed
8. Control Signals
Clock
One micro-instruction (or set of parallel micro-instructions) per clock cycle
Instruction register
Op-code for current instruction
Determines which micro-instructions are performed
Flags
State of CPU
Results of previous operations
From control bus
Interrupts
Acknowledgements
9. Control Signals - output
Within CPU
Cause data movement
Activate specific functions
Via control bus
To memory
To I/O modules
11. Hardwired Control
Design is based on a fixed architecture. The CU is
made up of flip-flops, logic gates, digital circuits and
encoder and decoder circuits that are wired in a
specific and fixed way. When instruction set changes
are required, wiring and circuit changes must be
made.
12. Microprogram control
Microprograms are stored in a special control
memory and are based on flowcharts. They are
replaceable and ideal because of their simplicity.