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Architechture of 8085 (Contd..)

Published on Jun 18 2014 // General Details of 8085

Arithmetic and Logic Unit (ALU):

  • It is used to perform the arithmetic operations like addition, subtraction, multiplication, division, increment and decrement and logical operations like AND, OR and EX-OR.
  • It receives the data from accumulator and registers.
  • According to the result it set or reset the flags.

Program Counter (PC):

  • This 16-bit register sequencing the execution of instructions.
  • It is a memory pointer. Memory locations have 16-bit addresses, and that is why this is a 16-bit register.
  • The function of the program counter is to point to the memory address of the next instruction to be executed.
  • When an opcode is being fetched, the program counter is incremented by one to point to the next memory location.

Stack Pointer (Sp):

  • The stack pointer is also a 16-bit register used as a memory pointer.
  • It points to a memory location in R/W memory, called the stack.
  • The beginning of the stack is defined by loading a 16-bit address in the stack pointer (register).

Temporary Register: It is used to hold the data during the arithmetic and logical operations.

Instruction Register:  When an instruction is fetched from the memory, it is loaded in the instruction register.

Instruction Decoder: It gets the instruction from the instruction register and decodes the instruction. It identifies the instruction to be performed.

Serial I/O Control:  It has two control signals named SID and SOD for serial data transmission.

Timing and Control unit:

  • It has three control signals ALE, RD (Active low) and WR (Active low) and three status signals IO/M(Active low), S0 and S1.
  • ALE is used for provide control signal to synchronize the components of microprocessor and timing for instruction to perform the operation.
  • RD (Active low) and WR (Active low) are used to indicate whether the operation is reading the data from memory or writing the data into memory respectively.
  • IO/M(Active low) is used to indicate whether the operation is belongs to the memory or peripherals.
  • If,

Interrupt Control Unit:

  • It receives hardware interrupt signals and sends an acknowledgement for receiving the interrupt signal.