Tuesday, 14 March 2023

Hardwired control unit (HCU)

Hardwired Control Unit(HCU)

It is one of the approach used for the control unit design. In the hardwired control, the control units use fixed logic circuit to interpret the instructions and generate the control signals from them. Figure shows the typical Hardwired control unit (HCU).
Here, the fixed logic circuit block includes combinational circuit that generates the required control O/P for decoding and encoding functions by separating the decoding and encoding functions.

 Various Methods to Design Hardwired Control Unit: The methods for designing the hardwired control units are using the gates, flip-flops, decoders, encoders and
other digital circuit.

Hardwired Control Unit (HCU)  by using the Decoder: the The use of a decoder can be used to build a Hardwired Control Unit (HCU). The decoder is a combinational circuit that outputs a series of control signals after receiving an instruction code as input. The numerous processes that the CPU must carry out in order to carry out the instruction are represented by the control signals produced by the decoder.

Each of the fields in the instruction code typically designates a certain operation or parameter. The first field in a common instruction code format for a computer's CPU, for instance, might specify the operation to be carried out, such as addition or subtraction, while the second field might indicate where the operands are located in memory or registers.

Each field of the instruction code is decoded separately to produce the control signals using a decoder. For each potential value of the field, the decoder creates a distinct output signal using the input code. The final set of control signals required to carry out the instruction are created by combining the output signals from each field decoder.

Consider, for example, a straightforward instruction code structure with the fields opcode and register address. The register address field defines the location of the operand in a register, while the opcode field describes the action to be carried out. Assume there are eight possible register addresses in addition to the four possible opcodes (00, 01, 10, and 11): 000, 001, 010, 011, 100, 101, and 110.

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