Computer Architecture: Accumulators and Registers

Study Notes

Accumulator

An 8-bit register that holds data for processing by the Arithmetic Logic Unit (ALU).
Stores results of operations and is also referred to as the A register.
Connected to an 8-bit internal data bus for data transfer.

Temporary Register

Receives data from external memory or general-purpose registers for the ALU.
Supplies one input to the ALU while the other input is from the accumulator.
Used for storing operands in arithmetic and logic operations.

General Purpose Registers

Six 8-bit general-purpose registers: B, C, D, E, H, and L.
Registers can be used individually or combined as pairs (BC, DE, HL) for 16-bit operations.
HL register pair typically serves as a 16-bit memory pointer.

Stack Pointer (SP)

A 16-bit register that maintains the address of the last byte entered into the stack.
Stack is a reserved area of RAM for temporary data storage.
Decrements on data entry and increments on data retrieval.

Program Counter (PC)

A 16-bit memory pointer that sequences instruction execution.
Points to the address of the next instruction.
Increments by one after executing an instruction to indicate the next location.

Incrementer-Decrementer

Can add or subtract one from the contents of the stack pointer or program counter.

Arithmetic and Logic Unit (ALU)

Executes arithmetic (addition, subtraction) and logic operations (AND, OR, XOR) on 8-bit data.
Inputs to the ALU are from the accumulator and the temporary register.
Stores results back in the accumulator.

Flags

Composed of five individual flip-flops indicating statuses after arithmetic and logic operations.

Instruction Register and Decoder

An 8-bit register that fetches and loads instructions from memory.
Instruction decoder decodes contents to determine operation execution and directs the timing and control unit.

Timing and Control Unit

Contains an oscillator generating two-phase clock signals (CLK and CLK bar) for synchronization of registers.
The controller sequencer is micro-programmed and contains ROM for storing micro-routines needed for instruction execution.

Interrupt Control

Manages temporary interruptions for input/output (I/O) device requests.
The main program execution is halted to process interrupt signals for data input.

Serial I/O Control

Manages serial data input and output for I/O devices.
Data enters the 8085 microprocessor through SID (serial input data) and exits through SOD (serial output data).
SIM and RIM instructions facilitate serial-parallel conversion for serial I/O operations.

Address Buffers

Contents of the stack pointer or program counter can be loaded into address buffers.
Outputs direct external address and address data buses, connecting memory and I/O chips to the CPU.
Enables the CPU to send addresses for desired data to memory or I/O devices.

Description

Explore the functions and characteristics of accumulators and temporary registers in computer architecture. This quiz covers their roles in the Arithmetic Logic Unit (ALU) and their connection to the internal data bus. Test your knowledge and understanding of these essential components of a computer system!