Page 63 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Unit 4: Microprocessor Architecture

processing performed by the processor. After the information has been processed by the ALU, it Notes
is sent to the computer memory.
In some computer processors, the ALU is divided into two distinct parts, the AU and the LU. The
AU performs the arithmetic operations and the LU performs the logical operations.

4.2.2 Accumulator
The Accumulator holds one of the operands as well as the result in operations performed by the
ALU.
Accumulator may refer to:

• Accumulator (computing), in a CPU, a processor register for storing intermediate results
• Accumulator (energy), an apparatus for storing energy or power
– Capacitor, in electrical engineering, also known by the obsolete term accumulator
– Electrochemical cell, a cell that stores electrical energy, typically used in rechargeable
batteries
– Hydraulic accumulator, an energy storage device using hydraulic fluid under pressure
• Accumulator (bet), a parlay bet

• Accumulator (structured product), a financial contract used by clients (usually individuals)
to accumulate stock positions over time

• Accumulator 1, a Czech film
• Dynamic accumulator, a plant that mines nutrients from the soil through its roots

4.2.3 Program Counter (PC)
The program counter contains the memory address of the next program instruction to be executed.

The program counter or PC (also called the instruction pointer to a seminal Intel instruction set,
such as the 8080 or 4004, or instruction address register, or just part of the instruction sequencer
in some computers) is a processor register that indicates where the computer is in its instruction
sequence. Depending on the details of the particular computer, the PC holds either the address of
the instruction being executed or the address of the next instruction to be executed.
In most processors, the program counter is incremented automatically after fetching a program
instruction so that instructions are normally retrieved sequentially from memory, with certain
instructions, such as branches, jumps and subroutine calls and returns, interrupting the sequence
by placing a new value in the program counter.
Such jump instructions allow a new address to be chosen as the start of the next part of the flow
of instructions from the memory. They allow new values to be loaded (written) into the program
counter register. A subroutine call is achieved simply by reading the old contents of the program
counter, before they are overwritten by a new value, and saving them somewhere in memory or
in another register. A subroutine return is then achieved by writing the saved value back into the
program counter again.

Give the basic concept of accumulator. Explain with example.

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