Explain hardwired control unit. What are the methods to design hardwired controllers ? OR What do you understand by hardwired control ? Give various methods to design hardwired control unit. Describe any one method used for designing of hardwired control unit.

Hardwired Control:

1. Definition:
   • Hardwired control is like a brain for a computer, designed as a sequential logic circuit or finite state machine.
   • It generates a series of control signals based on the instructions it receives.
2. Implementation:
   • Uses gates, flip-flops, decoders, and other digital circuits for its control logic.

1. Modification:
   • If you want to change the design, you have to physically alter the wiring among components.
2. Signal Transformation:
   • Transforms input logic signals into a set of output logic signals, known as control signals.
3. Clock Cycle:
   • Each step in the control sequence happens in one clock cycle.
4. Control Signals Determination:
   • Uses information like the control step counter, instruction register, condition code flags, and external input signals.

Methods for Designing Hardwired Control:

1. State Table (One-Hot) Method:
   • Represents control states in a table.
   • Each state is indicated by a single bit, simplifying the design.
2. Delay Element Method:
   • Uses delay elements to sequence control steps.
3. Sequence-Counter Method:
   • Utilizes a counter to keep track of control steps.
4. PLA Method (Programmable Logic Array):

PLA Method:

1. PLA Definition:
   • A digital system device that consolidates complex logic circuits into a single chip.
   • Replaces many smaller integration chips, reducing the overall complexity.
2. Implementation:
   • Decision logic and decoder functions are housed in the PLA.
3. Advantages:
   • Reduces the number of integrated circuits (ICs) and interconnection wires.
4. Role in Hardwired Control:
   • PLA outputs dictate the next state of the sequence register in hardwired control.