Stack is also known as the Last In First Out (LIFO) list. It is the most important feature in the CPU. It saves data such that the element stored last is retrieved first. A stack is a memory unit with an address register. This register influence the address for the stack, which is known as Stack Pointer (SP). The stack pointer continually influences the address of the element that is located at the top of the stack.It can insert an element into or delete an element from the stack. The insertion operation is known as push operation and the deletion ... Read More

A set of flip-flops forms a register. A register is a unique high-speed storage area in the CPU. They include combinational circuits that implement data processing. The information is always defined in a register before processing. The registers speed up the implementation of programs.Registers implement two important functions in the CPU operation are as follows −It can support a temporary storage location for data. This supports the directly implementing programs to have fast access to the data if required.It can save the status of the CPU and data about the directly implementing program.Example − Address of the next program instruction, ... Read More

CPU stands for Central Processing Unit. It is the soul of a computer system. The CPU along with the memory and the I/O sub-systems establish a strong computer system.A CPU includes small layers of hundreds of transistors. Transistors are microscopic bits of substances that block electricity at one voltage (non-conductor) and enable electricity to move through them at multiple voltages (conductor).These slight bits of substantial are the semiconductors that create two electronic inputs and create multiple outputs when one or both inputs are turned on.CPU is the most significant in a computer system. It is the component that regulates all ... Read More

The microinstructions can be determined by symbols. It is interpreted to its binary format with an assembler. The symbols should be represented for each field in the microinstruction. The users should be enabled to represent their symbolic addresses. Each line in an assembly language represents symbolic instruction. These instructions are divided into five fields such as label, micro-operations, CD, BR, and AD.The fields that specify the following information are as follows −The label field may be empty or it may specify a symbolic address. A label is terminated with a colon (:).The micro-operations field consists of one, two, or three ... Read More

A microinstruction format includes 20 bits in total. They are divided into four elements as displayed in the figure.F1, F2, F3 are the micro-operation fields. They determine micro-operations for the computer.CD is the condition for branching. They choose the status bit conditions.BR is the branch field. It determines the type of branch.AD is the address field. It includes the address field whose length is 7 bits.The micro-operations are divided into three fields of three bits each. These three bits can define seven different micro-operations. In total there are 21 operations as displayed in the table.Symbols with their Binary Code for ... Read More

The microcode for the control memory should be generated by the inventor once the configuration of the computer is settled. The generation of code is known as microprogramming.There are various points to be treated while designing the microprogram sequencer are −Size of the microinstructionTime of address generationThe microinstruction’s size should be in the least, therefore that the control memory necessary is less and the cost is decreased. Microinstructions can be implemented at a quicker rate if the time to create an address is less. This results in raised throughput.Disadvantage of Micro-program SequencingThe disadvantage of microprogram sequencing is as follows −If ... Read More

Subroutines are programs that are used by other routines to accomplish a particular task. A subroutine can be called from any point within the main body of the micro-program. Frequently, many micro-programs contain identical sections of code. Microinstructions can be saved by employing subroutines that use common sections of microcode.For example, the sequence of micro-operations needed to generate the effective address of the operand for instruction is common to all memory reference instructions. This sequence could be a subroutine that is called from within many other routines to execute the effective address computation.Micro-programs that use subroutines must have a provision ... Read More

A unique type of branch exists when a microinstruction defines a branch to the first word in control memory where a micro-program routine for instruction is placed. The status bits for this type of branch are the bits in the operation code part of the instruction. For example, a computer with a simple instruction format as shown in the figure.It has an operation code of four bits which can specify up to 16 distinct instructions. It can consider that the control memory has 128 words, needing an address of seven bits. For each operation code, there exists a micro-program routine ... Read More

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