The Wilkes Control Unit is a part of the Electronic Delay Storage Automatic Calculator (EDSAC), one of the early computers designed by Sir Maurice Wilkes in the late 1940s. The control unit is responsible for coordinating the execution of instructions by generating control signals for various components within the computer.
Functioning of the Wilkes Control Unit:
1. Instruction Decoding: The control unit decodes the instruction fetched from memory to determine the required sequence of micro-operations.
2. Control Signals Generation: Based on the instruction, the control unit generates control signals that activate or deactivate various components in the computer, such as ALU, registers, and memory.
3. Micro-Operation Sequencing: The control unit sequences the micro-operations to be performed by different components in a synchronized manner.
4. Address Generation: In the case of memory access, the control unit generates the memory address for read or write operations.
5. Status Monitoring: The control unit monitors the status of different components and signals to detect conditions like overflow, carry, or other status flags.
Format of the Control Memory:
The control memory is a crucial part of the Wilkes Control Unit and stores the microcode that specifies the control signals for each instruction. The format of the control memory typically consists of fields for different control signals.
Components of the Control Memory Format:
1. Instruction Opcode Field: Identifies the instruction being executed.
2. Micro-Operation Fields: Specify the micro-operations corresponding to the instruction. These fields encode the control signals for ALU operations, register transfers, memory operations, etc.
3. Next Address Field: Indicates the address of the next microinstruction to be executed. It enables the sequencing of micro-operations.
4. Condition Fields: Include conditions or flags that determine whether certain micro-operations should be executed based on the status of the machine.
5. Control Signals Fields: Represent various control signals that are activated or deactivated during the execution of the instruction.
The control memory format is crucial for the proper execution of instructions and ensures that the control unit coordinates the operation of the computer's components in a precise and synchronized manner.
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