A conditional branch instruction is a branch instruction that may or may not generate a transmission of control that relies upon the value of stored bits in the PSR (processor status register). It provides decision-making capabilities in the control unit.The status conditions are special bits in the system that provide parameter information such as the carry-out of an adder, the sign bit of a number, the mode bits of instruction, and input or output status conditions. Information in these bits can be tested and actions initiated based on their condition: whether their value is 1 or 0.The status bits, together ... Read More

Microinstructions are saved in control memory in groups. These groups describe routines. Each computer instruction has its microprogram routine that can create micro-operations. These micro-operations can execute instructions. The hardware consists of controls for the address sequencing of the microinstructions of a similar routine. They also branch the microinstructions.There are the following phases that the control has while implementing a computer instruction −When power is turned on, and address is initially loaded into the control address register. (This is the address of the first microinstruction).The control address register is incremented resulting in sequencing the fetch routine.After the fetch routine, the ... Read More

Hardwired Control UnitA hardwired control is a structure of making control signals using Finite State Machines (FSM) suitably. It is created as a sequential logic circuit. The final circuit is generated by physically linking the components including gates, flip flops, and drums are known as the hardwired controller.Microprogrammed Control UnitA control unit whose binary control values are saved as words in memory is called a microprogrammed control unit.In these instructions, the control memory is considered to be ROM, where all the information is saved permanently. The memory address of the control unit denotes the address of microinstruction.The microinstruction has a ... Read More

A control unit whose binary control values are saved as words in memory is called a microprogrammed control unit.A controller results in the instructions to be implemented by constructing a definite collection of signals at each system clock beat. Each of these output signals generates one micro-operation including register transfer. Thus, the sets of control signals are generated definite micro-operations that can be saved in the memory.Each bit that forms the microinstruction is linked to one control signal. When the bit is set, the control signal is active. When it is cleared the control signal turns inactive. These microinstructions in ... Read More

A hardwired control is a mechanism of producing control signals using Finite State Machines (FSM) appropriately. It is designed as a sequential logic circuit. The final circuit is constructed by physically connecting the components such as gates, flip flops, and drums. Hence, it is named a hardwired controller.The figure shows a 2-bit sequence counter, which is used to develop control signals. The output obtained from these signals is decoded to generate the required signals in sequential order.The hardwired control consists of a combinational circuit that outputs desired controls for decoding and encoding functions. The instruction that is loaded in the ... Read More

A control memory is a part of the control unit. Any computer that involves microprogrammed control consists of two memories. They are the main memory and the control memory. Programs are usually stored in the main memory by the users. Whenever the programs change, the data is also modified in the main memory. They consist of machine instructions and data.The control memory consists of microprograms that are fixed and cannot be modified frequently. They contain microinstructions that specify the internal control signals required to execute register micro-operations.The machine instructions generate a chain of microinstructions in the control memory. Their function ... Read More

A control unit drives the corresponding processing hardware by generating a set of signals that are in sync with the master clock. The two major operations performed by the control unit are instruction interpretation and instruction sequencing.The control unit is a part of the Central Processing Unit (CPU). The CPU is divided into the arithmetic logic unit and the control unit. The control unit generates the appropriate timing and control signals to all the operations involved with a computer. The flow of data between the processor, memory, and other peripherals is controlled using the timing signals of the control unit.The ... Read More

A bus is a structure that handles the data transmission in a computer system or network. The common bus of 16-bit is controlled by the selection inputs S2, S1 , and, S0.Each binary number is associated with a Boolean variable x1 through x7, corresponding to the gate structure that must be active to select the register or memory for the bus.For example, when x1 = 1, the value of S2, S1 , and, S0 must be 001 and the output of AR will be selected for the bus.The decimal number shown with each bus input indicates the binary equivalent that ... Read More

Flip flops are an application of logic gates. A flip-flop is a basic memory element that can save one bit of data. Flip flop has two stable states. One of the stable states is called SET or 1. The other stable state is known as RESET, CLEAR, or 0.A flip-flop circuit can stay in a binary state continually (as long as power is transferred to the circuit) before conducted by an input signal to switch states. The control gates for the seven flip-flops can be determined similarly. For example, the table shows that IEN may change as a result of ... Read More

The control inputs to registers and memory are −Load (LD) − When it is enabled, the content from the source register or memory can be transferred to/from the bus.Increment (INR) − It can increment the register by 1.Clear (CLR) − It can clear the register.The figure shows a scheme for the control of registers and memory.As shown in the diagram, all the register transfer statements are checked originally which modifies the content of AR.The instructions are as follows −R′T0:AR ← PCR′T2:AR ← IR(0 − 11)D′7IT3 :AR ← M[AR]RT0:AR ← 0D5T4:AR ← AR + 1The first three statements determine the transfer ... Read More